second letter of the Latin alphabet, corresponding to Greek beta, Phoenician beth, literally "house." It "has nothing of that variety of pronunciation shown by most English letters" [Century Dictionary]. The Germanic "b" is said to represent a "bh" sound in Proto-Indo-European, which continued as "bh" in Sanskrit, became "ph" in Greek (brother/Greek phrater; bear (v.)/Greek pherein) and "f" in Latin (frater, ferre).

Often indicating "second in order." B-movie is by 1939, usually said to be so called from being the second, or supporting, film in a double feature. Some film industry sources say it was so called for being the second of the two films major studios generally made in a year, and the one cast with less headline talent and released with less promotion. And early usage varies with grade-B movie, suggesting a perceived association with quality.

B-side of a gramophone single is by 1962 (flip-side is by 1949). B-girl, abbreviation of bar girl, U.S. slang for a woman paid to encourage customers at a bar to buy her drinks, is by 1936.

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Definitions of B from WordNet

b (n.)
aerobic rod-shaped spore-producing bacterium; often occurring in chainlike formations; found primarily in soil;
Synonyms: bacillus
b (n.)
originally thought to be a single vitamin but now separated into several B vitamins;
Synonyms: B-complex vitamin / B complex / vitamin B complex / vitamin B / B vitamin
b (n.)
a trivalent metalloid element; occurs both in a hard black crystal and in the form of a yellow or brown powder;
Synonyms: boron / atomic number "
b (n.)
a logarithmic unit of sound intensity equal to 10 decibels;
Synonyms: Bel
b (n.)
(physics) a unit of nuclear cross section; the effective circular area that one particle presents to another as a target for an encounter;
Synonyms: barn
b (n.)
the blood group whose red cells carry the B antigen;
Synonyms: type B / group B