Old English flint "flint; a type of rock noted for hardness and for giving off sparks when struck," from Proto-Germanic *flintaz (source also of Middle Dutch vlint, Old High German flins, Danish flint), from PIE *splind- "to split, cleave," from root *(s)plei- "to splice, split" (source also of Greek plinthos "brick, tile," Old Irish slind "brick"), perhaps a variant of *spel- (1) "to split, break off." Transferred senses (hardness, etc.) were in Old English.
"miser, one who makes use of contemptible economy to keep money," 1700, slang; literally "kind of person who would skin a flint to save or gain something," from skin (v.) + flint. Flay-flint in same sense is from 1670s. Among the 18c. slang terms for a miserly person was nipcheese (1785, originally "a ship's purser").
"flat, square table or slab under the molding of the base of a Roman column; square molding at the base of any architectural part," 1610s, from French plinthe (16c.) and directly from Latin plinthus, from Greek plinthos "brick, squared stone," from PIE *splind- "to split, cleave," from root *(s)plei- "to splice, split" (see flint).
1580s (transitive and intransitive), not found in Middle English, probably from a Low German source such as Middle Dutch splitten, from Proto-Germanic *spleitanan (source also of Danish and Frisian splitte, Old Frisian splita, German spleißen "to split"), from PIE *(s)plei- "to split, splice" (see flint).
U.S. slang meaning "leave, depart" first recorded 1954. Of couples, "to separate, to divorce" from 1942. To split the difference is suggested from 1715; to split (one's) ticket in the U.S. political sense is attested from 1842. To split hairs "make too-nice distinctions" is from 1670s (split a hair; the figurative image itself is implied in Shakespeare). Splitting image "exact likeness" is from 1880. To split the atom is from 1909.