To stimulate or excite something from the outside or from an external source.
From Latin 'ex-' (out, from) + 'stimulare' (to poke, goad, stimulate). This rare verb was more common in 17th-18th century scientific writing but remains largely obsolete.
Before 'external stimulation' became standard terminology, scientists would write about how light extimulates the eye—it's basically the same concept but in beautifully archaic Latin-rooted language!
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