'loosely-packed' is a compound formed from 'loosely' and 'packed'. 'loosely' derives from Old English/Middle English 'lōs'/'loos' (Old English 'lōs' meaning 'free' or 'unbound') with the adverbial/derivational suffix '-ly' from Old English '-līc' meaning 'like' or 'characteristic of'. 'packed' comes from the verb 'pack', which traces to Middle English 'pakken/packen' (from a Germanic root meaning 'to bind or bundle together').

'loosely-packed' developed as a modern English compound from the adverb 'loosely' (Middle English 'loos' from Old English 'lōs') combined with the past-participial adjective 'packed' (from Middle English 'packen'/'pakken', from a Proto-Germanic packing verb). Over time these elements combined in Modern English to form the descriptive compound 'loosely-packed'.

Originally, the verb 'pack' meant simply 'to put into a pack or bundle'. Over time 'packed' also came to mean 'densely filled or crowded'. The compound 'loosely-packed' therefore evolved to specify the opposite sense: 'arranged or filled but not densely—having noticeable space between parts.'