late 14c., "possible" (as opposed to actual), "capable of being or becoming," from Old French potenciel and directly from Medieval Latin potentialis "potential," from Latin potentia "power, might, force;" figuratively "political power, authority, influence," from potens "powerful," from potis "powerful, able, capable; possible;" of persons, "better, preferable; chief, principal; strongest, foremost," from PIE root *poti- "powerful; lord."
The noun, meaning "that which is possible, anything that may be" is attested by 1817 (Coleridge), from the adjective. Middle English had potencies (plural) "a caustic medicine" (early 15c.).
"the making actual, by an exertion of will, that which lies dormant in one's soul; the fulfilment, by one's own effort, of the potential in one's soul," 1839, from self- + realization.
early 14c., "pertaining to acts or an action;" late 14c. in the broader sense of "real, existing" (as opposed to potential, ideal, etc.); from Old French actuel "now existing, up to date" (13c.), from Late Latin actualis "active, pertaining to action," adjectival form of Latin actus "a doing" (from PIE root *ag- "to drive, draw out or forth, move").
"1.5-ounce shot glass," 1836, American English, in early use also of the drink itself, probably from jigger "illicit distillery" (1824), a word of unknown origin. Or else perhaps from jigger (n.2) "tiny mite or flea." As a name for various appliances the word is attested by 1726, from jig. In telegraphy it was a small transformer used for regulating and maintaining the difference of potential between terminals.