means To rub or scrape a surface, often with nails or claws, to relieve an itch or leave a mark — or, as a noun, the small wound or line such scraping leaves.

from From Middle English, where two older words seem to have collided and merged: 'scratten' (to scratch) and 'cracchen' (to claw), both echoing the harsh, grating sound of the act itself. They trace back to Germanic roots possibly related to Old High German 'krazzon,' a cousin to modern German 'kratzen,' to scratch. The many idioms — 'from scratch,' 'up to scratch,' 'scratch the surface' — grew later, several borrowed from the starting lines once scratched into the ground for races and prizefights.