c.1300, from Old French
as "one at dice", from Latin as (genitive assis) "a unit", from the name of a small Roman coin, perhaps originally Etruscan and related to Greek eis "one." It meant the side of the die with only one mark before it meant the playing card. Since this was the lowest roll at dice, ace was used metaphorically in Middle English
for "bad luck;" but as the ace is often the highest playing card, the extended senses based on "excellence, good quality" arose 18c. as card-playing became popular. Meaning "outstanding pilot" dates from 1917 (technically, in WWI aviators' jargon, one who has brought down 10 enemy planes). Sports meaning of "point scored" (1819) led to that of "unreturnable serve" (1889). The verb meaning "to score" (in sports) is first attested 1923, and led to the extended student slang sense of "get high marks" (1959). Ace in the hole "concealed advantage" is attested from 1915.