Noun
the 1st letter of the Roman alphabet

Noun
the blood group whose red cells carry the A antigen

Noun
the basic unit of electric current adopted under the Systeme International d''Unites; "a typical household circuit carries 15 to 50 amps"

Noun
a metric unit of length equal to one ten billionth of a meter (or 0.0001 micron); used to specify wavelengths of electromagnetic radiation

Noun
(biochemistry) purine base found in DNA and RNA; pairs with thymine in DNA and with uracil in RNA

Noun
one of the four nucleotides used in building DNA; all four nucleotides have a common phosphate group and a sugar (ribose)

Noun
any of several fat-soluble vitamins essential for normal vision; prevents night blindness or inflammation or dryness of the eyes

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The first letter of the English and of many other alphabets. The capital A of the alphabets of Middle and Western Europe, as also the small letter (a), besides the forms in Italic, black letter, etc., are all descended from the old Latin A, which was borrowed from the Greek Alpha, of the same form; and this was made from the first letter (/) of the Phoenician alphabet, the equivalent of the Hebrew Aleph, and itself from the Egyptian origin. The Aleph was a consonant letter, with a guttural breath sound that was not an element of Greek articulation; and the Greeks took it to represent their vowel Alpha with the a sound, the Phoenician alphabet having no vowel symbols.

The name of the sixth tone in the model major scale (that in C), or the first tone of the minor scale, which is named after it the scale in A minor. The second string of the violin is tuned to the A in the treble staff. -- A sharp (A/) is the name of a musical tone intermediate between A and B. -- A flat (A/) is the name of a tone intermediate between A and G.

An adjective, commonly called the indefinite article, and signifying one or any, but less emphatically.

In each; to or for each; as, "twenty leagues a day", "a hundred pounds a year", "a dollar a yard", etc.

prep.
In; on; at; by.

prep.
In process of; in the act of; into; to; -- used with verbal substantives in -ing which begin with a consonant. This is a shortened form of the preposition an (which was used before the vowel sound); as in a hunting, a building, a begging.

Of.

A barbarous corruption of have, of he, and sometimes of it and of they.

An expletive, void of sense, to fill up the meter

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A

A (named 'be in the English, and most commonly '84 in other languages). The first letter of the English and of many other alphabets. The capital A of the alphabets of Middle and Western Europe, as also the small letter (a), besides the forms in Italic, black letter, etc., are all descended from the old Latin A, which was borrowed from the Greek Alpha, of the same form; and this was made from the first letter (Aleph, and itself from the Egyptian origin. The Aleph was a consonant letter, with a guttural breath sound that was not an element of Greek articulation; and the Greeks took it to represent their vowel Alpha with the '84 sound, the Ph'd2nician alphabet having no vowel symbols. This letter, in English, is used for several different vowel sounds. See Guide to pronunciation, §§ 43-74. The regular long a, as in fate, etc., is a comparatively modern sound, and has taken the place of what, till about the early part of the 17th century, was a sound of the quality of '84 (as in far). 2. (Mus.) The name of the sixth tone in the model major scale (that in C), or the first tone of the minor scale, which is named after it the scale in A minor. The second string of the violin is tuned to the A in the treble staff. -- A sharp (A) is the name of a musical tone intermediate between A and B. -- A flat (A♭) is the name of a tone intermediate between A and G. A per se (L. per se by itself), one pre'89minent; a nonesuch. [Obs.]

O fair Creseide, the flower and A per se Of Troy and Greece.

A

A ( emph. ). 1. [Shortened form of an. AS. 'ben one. See One.] An adjective, commonly called the indefinite article, and signifying one or any, but less emphatically. "At a birth"; "In a word"; "At a blow". Shak. It is placed before nouns of the singular number denoting an individual object, or a quality individualized, before collective nouns, and also before plural nouns when the adjective few or the phrase great many or good many is interposed; as, a dog, a house, a man; a color; a sweetness; a hundred, a fleet, a regiment; a few persons, a great many days. It is used for an, for the sake of euphony, before words beginning with a consonant sound [for exception of certain words beginning with h, see An]; as, a table, a woman, a year, a unit, a eulogy, a ewe, a oneness, such a one, etc. Formally an was used both before vowels and consonants. 2. [Originally the preposition a (an, on).] In each; to or for each; as, "twenty leagues a day", "a hundred pounds a year", "a dollar a yard", etc.

A

A , prep. [Abbreviated form of an (AS. on). See On.] 1. In; on; at; by. [Obs.] "A God's name." "Torn a pieces." "Stand a tiptoe." "A Sundays" Shak. "Wit that men have now a days." Chaucer. "Set them a work." Robynson (More's Utopia) 2. In process of; in the act of; into; to; -- used with verbal substantives in -ing which begin with a consonant. This is a shortened form of the preposition an (which was used before the vowel sound); as in a hunting, a building, a begging. "Jacob, when he was a dying" Heb. xi. 21. "We'll a birding together." " It was a doing." Shak. "He burst out a laughing." Macaulay. The hyphen may be used to connect a with the verbal substantive (as, a-hunting, a-building) or the words may be written separately. This form of expression is now for the most part obsolete, the a being omitted and the verbal substantive treated as a participle.

A

A. [From AS. of off, from. See Of.] Of. [Obs.] "The name of John a Gaunt." "What time a day is it ?" Shak. "It's six a clock." B. Jonson.

A

A. A barbarous corruption of have, of he, and sometimes of it and of they. "So would I a done" "A brushes his hat." Shak.

A

A. An expletive, void of sense, to fill up the meter

A merry heart goes all the day, Your sad tires in a mile-a.

A 1

A 1 . A registry mark given by underwriters (as at Lloyd's) to ships in first-class condition. Inferior grades are indicated by A 2 and A 3. A 1 is also applied colloquially to other things to imply superiority; prime; first-class; first-rate.

The first letter of the English and of many other alphabets. The capital A of the alphabets of Middle and Western Europe, as also the small letter (a), besides the forms in Italic, black letter, etc., are all descended from the old Latin A, which was borrowed from the Greek Alpha, of the same form; and this was made from the first letter (Aleph, and itself from the Egyptian origin. The Aleph was a consonant letter, with a guttural breath sound that was not an element of Greek articulation; and the Greeks took it to represent their vowel Alpha with the '84 sound, the Ph'd2nician alphabet having no vowel symbols.

An adjective, commonly called the indefinite article, and signifying one or any, but less emphatically.

In; on; at; by.

Of.

A barbarous corruption of have, of he, and sometimes of it and of they.

An expletive, void of sense, to fill up the meter

A registry mark given by underwriters (as at Lloyd's) to ships in first-class condition. Inferior grades are indicated by A 2 and A 3.