title of honor of a knight or baronet (until 17c. also a title of priests), c. 1300, a variant of sire (q.v.) that was used originally only in unstressed position. It is not an acronym of anything.

It was generalized as a respectful form of address by mid-14c., and eventually extended to all equals or used without regard for rank. It has been used as a salutation at the beginning of letters from early 15c. As a noun, "person of rank or importance," from 14c.

suffix forming adjectives from nouns and meaning "having qualities of, of the form or nature of" (manly, lordly), "appropriate to, fitting, suited to" (bodily, earthly, daily); irregularly descended from Old English -lic, from Proto-Germanic *-liko- (Old Frisian -lik, Dutch -lijk, Old High German -lih, German -lich, Old Norse -ligr), related to *likom- "appearance, form" (Old English lich "corpse, body;" see lich, which is a cognate; see also like (adj.), with which it is identical).

late 14c., "haughty, imperious," from Old English hlafordlic "of or pertaining to lords, noble;" see lord (n.) + -ly (1). From 1530s as "magnificent, on a grand scale, fit for a lord." As an adverb, "despotically," from mid-14c.

Proto-Indo-European root meaning "old."

It forms all or part of: monseigneur; seignior; senate; senescent; seneschal; senicide; senile; senility; senior; seniority; senor; senora; senorita; shanachie; Shannon; signor; sir; sire; surly.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit sanah "old;" Avestan hana- "old," Old Persian hanata- "old age, lapse of time;" Armenian hin "old;" Greek enos "old, of last year;" Latin senilis "of old age," senex "old, old man;" Lithuanian senas "old," senis "an old man;" Gothic sineigs "old" (used only of persons), sinistra "elder, senior;" Old Norse sina "dry standing grass from the previous year;" Old Irish sen, Old Welsh hen "old."