Words related to *pet-
late 14c., "suitable, answering all requirements, sufficient, adequate," from Old French competent "sufficient, appropriate, suitable," and directly from Latin competentem (nominative competens), present participle of competere "coincide, agree" (see compete). It preserves the classical Latin sense of the verb, whereas the meaning in compete is a post-classical evolution. Meaning "able, fit, having ability or capacity" is from 1640s. Legal sense "having legal capacity or qualification" is late 15c. Related: Competently.
Old English feðer "a feather; a pen," in plural, "wings," from Proto-Germanic *fethro (source also of Old Saxon fethara, Old Norse fioþr, Swedish fjäder, Middle Dutch vedere, Dutch veder, Old High German fedara, German Feder), from PIE *pet-ra-, from root *pet- "to rush, to fly."
Feather-headed "silly" is from 1640s. Feather-duster attested by 1835. Figurative use of feather in (one's) cap attested by 1734. Birds of a feather "creatures of the same kind" is from 1580s; the same image is in Greek homopteros (variant birds of a beak is from c. 1600).
1861, from French hélicoptère "device for enabling airplanes to rise perpendicularly," thus "flying machine propelled by screws." From a Latinized combining form of Greek helix (genitive helikos) "spiral" (see helix) + pteron "wing" (from PIE root *pet- "to rush, to fly").
The idea was to gain lift from spiral aerofoils, and it didn't work. Used by Jules Verne and the Wright Brothers, the word was transferred to helicopters in the modern sense by 1918 when those began to be developed. Nativized in Flemish as wentelwiek "with rotary vanes."
omnivorous ungulate pachydermatous mammal of Africa, 1560s, from Late Latin hippopotamus, from Greek hippopotamus "riverhorse," an irregular formation from earlier ho hippos potamios "the horse of the river"), from hippos "horse" (from PIE root *ekwo- "horse") + adjective from potamos "river, rushing water" (see potamo-). Replaced Middle English ypotame (c. 1300), which is from the same source but deformed in Old French. Glossed in Old English as sæhengest. Translated as river-horse in Holland's Pliny (1601).
Ypotamos comen flyngynge. ... Grete bestes and griselich ["Kyng Alisaunder," c. 1300]
early 15c., impetous "rapid movement, rush;" 1640s, with modern spelling, "force with which a body moves, driving force," from Latin impetus "an attack, assault; rapid motion; an impulse; violence, vigor, force;" figuratively "ardor, passion," from impetere "to attack," from assimilated form of in- "into, in, on, upon" (from PIE root *en "in") + petere "aim for, rush at" (from PIE root *pet- "to rush, to fly").