1580s, "slight skin tear produced by a sharp thing," from scratch (v.). Meaning "mark or slight furrow in metal, etc." is from 1660s. American English slang sense of "money" is from 1914, of uncertain signification. Many figurative senses (such as up to scratch, originally "ready to meet one's opponent") are from sporting use for "line or mark drawn as a starting place," attested from 1778 (but the earliest use is figurative); meaning "nothing" (as in from scratch) is 1918, generalized from specific 19c. sporting sense of "starting point of a competitor who receives no odds in a handicap match." Sense in billiards is from 1850. Scratch-pad is attested from 1883.
