early 14c. "relative freedom of a noble metal from alloy or other impurities," from Anglo-French alai, Old French aloi "alloy," from aloiier (see alloy (v.)). Meaning " base metal alloyed with a noble metal" is from c. 1400. Modern spelling from late 17c. Meaning "any mixture of metals," without reference to values is from 1827.
c. 1400, "mix (a metal) with a baser metal," from Old French aloiier, aliier "assemble, join," from Latin alligare "bind to, tie to," from ad "to" (see ad-) + ligare "to bind, bind one thing to another, tie" (from PIE root *leig- "to tie, bind"). In figurative use often implying debasement or reduction. Meaning "to mix any two metals" without reference to values is from 1822. Related: Alloyed; alloying.