counter (n.)

mid-14c., "table where a money lender does business," from Old French contouer, comptoir (14c.) "counting room, table of a bank," from Medieval Latin computatorium "place of accounts," from Latin computatus, past participle of computare (see compute). Generalized 19c. from banks to shops, then extended to display cases for goods. Phrase under the counter is from 1926.

counter (v.)

"go against," late 14c., from Old French countre "facing opposite" (see counter-). Related: Countered; countering. As an adverb, from mid-15c.; as an adjective, from 1590s.