Done automatically or naturally without thinking, based on an inborn drive rather than learned behavior.
From Latin 'instinctus' (driven, impelled) based on 'instinguere' (to instigate). The suffix '-ive' makes it an adjective, and '-ly' converts it to an adverb. The meaning evolved from 'driven by impulse' to 'natural inborn behavior'.
Your instinctive fear of snakes and spiders exists even in babies who've never seen them—it's a survival instinct hardwired into human DNA over millions of years of evolution!
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