half-measure (n.)

Old English half, halb (Mercian), healf (W. Saxon) "side, part," not necessarily of equal division (original sense preserved in behalf), from Proto-Germanic *halba- "something divided" (source also of Old Saxon halba, Old Norse halfr, Old Frisian, Middle Dutch half, German halb, Gothic halbs "half"), a word of no certain etymology. Perhaps from PIE root *skel- (1) "to cut," or perhaps a substratum word. Noun, adjective, and adverb all were in Old English.

Used also in Old English phrases, as in modern German, to mean "one half unit less than," for example þridda healf "two and a half," literally "half third." The construction in two and a half, etc., is first recorded c. 1200. Of time, in half past ten, etc., first attested 1750; in Scottish, the half often is prefixed to the following hour (as in German, halb elf = "ten thirty").

To go off half-cocked in the figurative sense "speak or act too hastily" (1833) is in allusion to firearms going off prematurely; half-cocked in a literal sense "with the cock lifted to the first catch, at which position the trigger does not act" is recorded by 1750. In 1770 it was noted as a synonym for "drunk." Bartlett ("Dictionary of Americanisms," 1848) writes that it was "a metaphorical expression borrowed from the language of sportsmen, and is applied to a person who attempts a thing in a hurry without due preparation, and consequently fails."

c. 1200, "moderation, temperance, abstemiousness;" c. 1300, "instrument for measuring," from Old French mesure "limit, boundary; quantity, dimension; occasion, time" (12c.), from Latin mensura "a measuring, a measurement; thing to measure by," from mensus, past participle of metiri "to measure," from PIE root *me- (2) "to measure." The native word was Old English cognate mæð "measure."

Meaning "size or quantity as ascertained by measuring" is from early 14c. Meanings "action of measuring; standard measure of quantity; system of measuring; appointed or allotted amount of anything" are from late 14c. Also from late 14c. are the senses "proper proportion; balance." Sense of "that to which something is compared to determine its quantity" is from 1570s.

In music, from late 14c. as "air, tune;" 1570s as "rhythmic pattern." Specifically as "a group of tones indicated between two primary beats" is from 1660s. From mid-15c. as "rhythmic pattern in poetry;" c. 1500 in dance. Meaning "treatment 'meted out' to someone" is from 1590s; that of "plan or course of action intended to obtain some goal" is from 1690s; sense of "legislative enactment" is from 1759. Figurative phrase for good measure is from good measure as "ample in quantity in goods sold by measure" (late 14c.).