late Middle English: from Jack, pet form of the given name John. The term was used originally to denote an ordinary man (sense 6), also a youth (mid 16th cent.), hence the 'knave' in cards and 'male animal'. The word also denoted various devices saving human labour, as though one had a helper (senses 1, 3, 9, and 10 , and in compounds such as jackhammer and jackknife); the general sense 'labourer' arose in the early 18th cent. and survives in cheapjack, lumberjack, steeplejack, etc. Since the mid 16th cent. a notion of 'smallness' has arisen, hence senses 4, 5, 7, and 13 .late 19th cent.: from jack up 'give up'.1990s: from hijack.