From WordNet (r) 2.0 (August 2003) [wn]:
J
n 1: a unit of electrical energy equal to the work done when a
current of one ampere passes through a resistance of one
ohm for one second [syn: joule, J, watt second]
2: the 10th letter of the Roman alphabet [syn: J]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
J \J\ (j[=a]).
J is the tenth letter of the English alphabet. It is a later
variant form of the Roman letter I, used to express a
consonantal sound, that is, originally, the sound of English
y in yet. The forms J and I have, until a recent time, been
classed together, and they have been used interchangeably.
[1913 Webster]
Note: In medical prescriptions j is still used in place of i
at the end of a number, as a Roman numeral; as, vj,
xij. J is etymologically most closely related to i, y,
g; as in jot, iota; jest, gesture; join, jugular, yoke.
See I. J is a compound vocal consonant, nearly
equivalent in sound to dzh. It is exactly the same as g
in gem. See Guide to Pronunciation, [sect][sect] 179,
211, 239.
[1913 Webster]