'pillbug-like' originates from modern English, specifically the compound 'pillbug' plus the suffix '-like', where 'pillbug' referred to a small terrestrial crustacean and '-like' meant 'having the form or characteristics of'.

'pillbug' is a compound formed in modern English from 'pill' (referring to the rounded 'pill' shape when the animal curls) + 'bug' (an informal term for small creatures); the adjectival suffix '-like' comes from Old English 'līc' via Middle English and has been used to form likeness adjectives (for example, 'childlike'). Together they formed the descriptive compound 'pillbug-like'.

Initially it described something having qualities or appearance of a pillbug; this core meaning has remained stable and still means 'resembling a pillbug'.