Rampant means 'a wide spread', speedy effect on a vast expanse. Precise meaning – moving fast using hind legs, also brings out the meaning that it is speedy or galloping action. Example: The disease was rampant amongst the birds in the poultry. Unchecked, unrestrained, un-suppressed growth are few synonyms for rampant. The adjective rampant has been the origin for words like rampancy and rampantly.