Rampant means spreading unchecked. Rampant inflation, rampant corruption, rampant growth.
It is almost always about something unwelcome — rampant disease, rampant speculation — and the word says that nothing is holding it back. In heraldry, rampant describes an animal reared on its hind legs, as in the Lion Rampant of Scotland, and that is the original sense: the spreading meaning came from the idea of rearing up unchecked. Note run rampant.
1adjectiverampantSpreading unchecked.
“Crime was rampant in the city, and people were afraid to go out at night.”
synonyms: unchecked, widespread
2adjectiverearedReared on the hind legs, in heraldry.
“The family crest shows a golden lion rampant on a red shield.”
rampant is a quality of unchecked spread.
Old French ramper meant to climb or rear up, which is the heraldic sense. The idea of something rearing without restraint gave the modern meaning.
Old French
ramper — to creep, climb
Middle English
rampand
English, today
rampant
Built from
From Middle English rampand, rampend, present participle of rampen (“to rise by climbing, shoot up, sprout, sty, ascend”), from Old French ramper (“to creep, climb”) (see below), equivalent to ramp + and or ramp + ant. Recorded since 1382, "standing on the hind legs" (as in heraldry), later, "fierce, ravenous" (1387). Compare Scots rampand (“rampant”). Alternatively from Middle English rampant, from Old French rampant, the present participle of ramper (“to creep, climb”), equivalent to ramp + ant. Old French ramper derives from Frankish rampōn, hrampōn (“to hook, grapple, climb”), from rampa, hrampa (“hook, claw, talon”), from Proto-Germanic hrempaną (“to curve, shrivel, shrink, wrinkle”).
Etymology from Wiktionary, CC BY-SA