The late 19th-century pairing of ‘crack’ and ‘jack’ to form ‘crackerjack’ topped off a long history for those words. ‘Cracker’ is an elongation of ‘crack,’ an adjective meaning ‘expert’ or ‘superior’ that dates from 1793. Prior to that, ‘crack’ was a noun meaning ‘something superior’ and a verb meaning ‘to boast.’ (That verb use evolved from ‘to crack a boast,’ which came from the sense of ‘crack’ meaning ‘to make a loud sharp sound.’) ‘Jack’ has been used for ‘man’ since the mid-1500s, as in ‘jack-of-all-trades.’ ‘Crackerjack’ entered English first as a noun (‘someone or something of excellence’), then as an adjective. You may also know ‘Cracker Jack’ as a snack of candied popcorn and peanuts. The copyrighted product name dates from the 1890s.