"training station for recruits," by 1941, U.S. Marines slang, said to be from boot (n.1) as slang for "recruit," which is attested by 1915 and supposedly dates from the Spanish-American War and is a synecdoche from boots "leggings worn by U.S. sailors."
Latin adverbial phrase, literally "by that very fact, by the fact itself," from neuter ablative of ipse "he, himself, self" + ablative of factum "fact" (see fact).
also cornrow, 1769 as "a row of corn," by 1971 as a style of hair braids, so called for the resemblance. The verb in this sense also is by 1971.