'jam-packed' originates from English, combining the verb 'jam' (to press or squeeze tightly) and the verb 'pack' (to fill tightly).

'jam' as a verb developed in the 18th century meaning 'to press or wedge'; 'pack' comes from Old English 'pæccan' and Middle English forms such as 'pakken', and the compound 'jam-pack' emerged in modern English to denote intense packing, later forming the adjective 'jam-packed'.

Initially the components referred to literal pressing and filling; over time the compound evolved to be used figuratively to mean 'extremely full or crowded'.