instinct: [15] The etymological notion underlying instinct (and also the closely related instigate) is of ‘goading onwards with a pointed stick’. Its ultimate source is Latin instinguere ‘urge onwards, incite’, a compound verb formed from the prefix in- ‘on’ and stinguere ‘prick, goad’. Source also of English distinct and extinct, this goes back to the same root, *stig-, as produced English stick and Latin stīgāre ‘prick, goad’, the ancestor of English instigate [16].
The noun derived from it, instinctus, originally meant ‘incitement, instigation’, but it eventually moved on to ‘impulse’, the sense it had when English acquired it. The more specialized ‘innate impulse’ developed in the mid 16th century. => distinct, extinct, instigate, stick
instinct (n.)
early 15c., "a prompting," from Latin instinctus "instigation, impulse," noun use of past participle of instinguere "to incite, impel," from in- "on" (see in- (2)) + stinguere "prick, goad," from PIE *steig- "to prick, stick, pierce" (see stick (v.)). Meaning "animal faculty of intuitive perception" is from mid-15c., from notion of "natural prompting." Sense of "innate tendency" is first recorded 1560s.