E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Something pricked or punctured into one. Distinguish is of the same root, and means to prick or puncture separately. Extinguish means to prick or puncture out. In all cases
the allusion is to marking by a puncture. At college the markers at the chapel doors still hold a pin in one hand, and prick with it the name of each man who enters. The word is used to express a natural impulse to do something; an inherent habit.
Although reason may be blended with instinct, the distinction between the two is sufficiently precise. Reason only acts upon a definite and often laboriously acquired knowledge of the relation between means and ends.Romanes: Encyclopædia Britannica, vol. xiii. p. 157 (ninth edition).