belt n.

Old English belt "belt; girdle; broad, flat strip or strap of material used to encircle the waist," from Proto-Germanic *baltjaz (source also of Old High German balz, Old Norse balti, Swedish bälte), an early Germanic borrowing from Latin balteus "girdle, sword belt," which is said by Varro to be an Etruscan word.

The transferred sense of "broad stripe encircling something with its ends joined" is from 1660s; that of "broad strip or tract" of any sort, without notion of encircling (as in Bible belt) is by 1808. As a mark of rank or distinction, mid-14c.; references to boxing championship belts date from 1812. The mechanical sense is from 1795.

Below the belt "unfair" (1889) is from pugilism. To get something under (one's) belt was originally literal, to get it into one's stomach (1839), figurative use of that us by 1931. To tighten (one's) belt "endure privation" is from 1887.

early 14c., "to fasten or gird with a belt," from belt (n.). The meaning "to thrash as with a belt" is from 1640s; the general sense of "to hit, thrash" is attested from 1838. The colloquial meaning "to sing or speak vigorously" is from 1949. Related: Belted; belting. Hence (from the "thrash with a belt" sense) the noun meaning "a blow or stroke" (1885).