Origin and history of trend

1590s, "to run or bend in a certain direction" (of rivers, coasts, etc.), a sense developed from Middle English trenden "to roll (someone or something) over or about; turn, revolve," which is from Old English trendan "turn round, revolve, roll."

This is reconstructed to be from Proto-Germanic *trandijan (source also of Old English trinde "round lump, ball," Old Frisian trind, Middle Low German trint "round," Middle Low German trent "ring, boundary," Dutch trent "circumference," Danish trind "round"), but the origin and connections outside Germanic are uncertain.

The figurative sense of "have a general tendency, turn in some direction" (of affairs, opinions, etc.) is recorded by 1863, from the nautical sense. Related: Trended; trending.

1777, "general course or direction; the way something bends" (a coastline, mountain range, etc.), earlier "a round bend of a stream" (1620s); from trend (v.).

The sense of "tendency, proclivity" (of affairs, opinion, etc.) is by 1884; the sense of "a prevailing new tendency in popular fashion or culture" is from c. 1950. In Middle English, trending (n.) meant "circular motion."