late 13c., from O.Fr. principal
(11c.), from L. principalis
"first in importance," from princeps
). The noun is c.1300 in the sense of "ruler;" mid-14c. in the sense of "money on which interest is paid;" 1827 as "person in charge of a public school," though meaning "head of a college or hall" was in English from mid-15c., and the basic sense of "chief, commander, ruler" is recorded from late 14c. Principally
"in the first place, mainly" is from mid-14c.