seemly adj.

c. 1200, impersonal, hit semeth (it seems), "it appears (that something is so);" also with adjectives or phrases, "to appear to be (in some condition), have or present an appearance of being," from Old Norse soema "to honor; to put up with; to conform to (the world, etc.)," a verb derived from the adjective soemr "fitting."

This is reconstructed to be from Proto-Germanic *somiz (source also of Old English som "agreement, reconciliation," seman "to conciliate," source of Middle English semen "to settle a dispute," literally "to make one;" Old Danish söme "to be proper or seemly"), from PIE *somi-, suffixed form of root *sem- (1) "one; as one, together with" (also compare same).

With other verbs (seem to be, etc.) from c. 1200. Sense of "appear to oneself, think oneself" is from 1630s. Also in Middle English "to present oneself, appear; be visible, be apparent" (late 14c.), hence, of a fact, etc., "be evident, apparent, or obvious." The sense of "be fitting or appropriate, be expedient" (c. 1300) is the etymological one, but it is obsolete except in derived seemly, unseemly. Related: Seemed; seeming.

Proto-Indo-European root meaning "one; as one, together with."

It forms all or part of: anomalous; anomaly; assemble; assimilate; ensemble; facsimile; fulsome; hamadryad; haplo-; haploid; hendeca-; hendiadys; henotheism; hetero-; heterodox; heterosexual; homeo-; homeopathy; homeostasis; homily; homo- (1) "same, the same, equal, like;" homogenous; homoiousian; homologous; homonym; homophone; homosexual; hyphen; resemble; same; samizdat; samovar; samsara; sangha; Sanskrit; seem; seemly; semper-; sempiternal; similar; simple; simplex; simplicity; simulacrum; simulate; simulation; simultaneous; single; singlet; singular; some; -some (1); -some (2); verisimilitude.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit sam "together," samah "even, level, similar, identical;" Avestan hama "similar, the same;" Greek hama "together with, at the same time," homos "one and the same," homios "like, resembling," homalos "even;" Latin similis "like;" Old Irish samail "likeness;" Old Church Slavonic samu "himself."

c. 1300, "visually unpleasing, unattractive, ugly;" mid-14c., "unfitting, indecent, inappropriate," from un- (1) "not" + seemly (adj.). Similar formation in Old Norse usoemiligr. Related: Unseemliness.