lox (n.)

"salmon," from Old English leax (see lox). Cognate with Middle Dutch lacks, German Lachs, Danish laks, etc.; according to OED the English word was obsolete except in the north and Scotland from 17c., reintroduced in reference to Scottish or Norwegian salmon.

early 13c., samoun, the North Atlantic salmon, from Anglo-French samoun, Old French salmun (Modern French saumon), from Latin salmonem (nominative salmo) "a salmon," probably originally "leaper," from salire "to leap" (see salient (adj.)), though some dismiss this as folk etymology. Another theory traces the Latin word to Celtic.

Thompson ["Glossary of Greek Fishes"] writes that "The Salmon does not enter the Mediterranean. It is not mentioned by any Greek author, nor by any Latin writer except those two" [Pliny and Ausonius].

It replaced Old English læx, from PIE *lax, the more usual word for the fish (see lox). The classical -l- was restored in English from 16c., though Scott still uses saumon. In reference to a pinkish-orange color like that of the flesh of the fish, it is recorded by 1786. Related: Salmonic.