chap (n.) Look up chap at
1570s, "customer," short for obsolete chapman "purchaser, trader" (see cheap). Colloquial sense of "lad, fellow" is first attested 1716 (compare slang tough customer).
chap (v.) Look up chap at
"to crack," mid-15c., chappen (intransitive) "to split, burst open;" "cause to crack" (transitive); perhaps a variant of choppen (see chop (v.), and compare strap/strop), or related to Middle Dutch kappen "to chop, cut," Danish kappe, Swedish kappa "to cut." Related: Chapped; chapping. The noun meaning "fissure in the skin" is from late 14c.