ruinous (adj.)

late Old English, "act of giving way and falling down" (a sense now obsolete), from Latin ruina "a collapse, a rushing down, a tumbling down" (source also of Old French ruine "a collapse," Spanish ruina, Italian rovina), which is a derivative of ruere "to rush, fall violently, collapse" (from PIE *reue- (2) "to smash, knock down, tear out, dig up;" see rough (adj.)).

The sense of "descent from a state of prosperity, degradation, downfall or decay of a person or society" is from late 14c. The general meaning "violent or complete destruction" (of anything), "a profound change so as to unfit a thing for use" (of one's principles, one's shirt, etc.) is by 1670s; the sense of "that which causes destruction or downfall" is from early 15c. The meaning "dishonor," of a woman, is from 1620s. Ruins "remains of a decayed building or town" is from mid-15c.; the same sense was in the Latin plural noun.