late 12c., "emit or perceive an odor," not found in Old English, perhaps cognate with Middle Dutch smolen, Low German smelen "to smolder" (see smolder). However, OED says "no doubt of Old English origin, but not recorded, and not represented in any of the cognate languages." Related: Smelled or smelt; smelling.
Smelling salts (1840), used to revive the woozy, typically were a scented preparation of carbonate of ammonia. Smell-feast (n.) "one who finds and frequents good tables, one who scents out where free food is to be had" is from 1510s ("very common" c. 1540-1700, OED). Smell-smock "licentious man" was in use c. 1550-c. 1900. To smell a rat "be suspicious" is from 1540s.