late 13c., salarie, "compensation, payment," whether periodical, for regular service or for a specific service; from Anglo-French salarie, Old French salaire "wages, pay, reward," from Latin salarium "an allowance, a stipend, a pension," said to be originally "salt-money, soldier's allowance for the purchase of salt" [Lewis & Short] noun use of neuter of adjective salarius "of or pertaining to salt; yearly revenue from the sale of salt;" as a noun, "a dealer in salt fish," from sal (genitive salis) "salt" (from PIE root *sal- "salt").
Over time by 19c. it became restricted to recompense stipulated to be paid a person periodically for services, usually a fixed sum. The Via Salaria was so called because the Sabines used it to fetch sea-salt near the Porta Collina. Japanese sarariman "male salaried worker," literally "salary-man," is from English.
"to pay a regular salary to," late 15c. (Caxton), from salary (n.). Related: Salaried "in receipt of a fixed salary" (c. 1600), which as an adjective in reference to positions originally was contrasted with honorary ("without pay"); from 20c. with hourly ("paid by the hour").