'lentil-shaped' originates from Modern English, specifically formed from the noun 'lentil' + the adjective-forming element 'shaped', where 'lentil' referred to the small legume.

'lentil' changed from Middle English/Old French 'lentille' (or Anglo-French) and ultimately from Latin 'lens, lentis', and eventually became the modern English noun 'lentil'; the compound 'lentil-shaped' is a later Modern English formation combining that noun with 'shaped'.

Initially, 'lentil' referred to the edible seed; over time the word has been used adjectivally in compounds (e.g. 'lentil-shaped') to mean 'having the shape of a lentil' (i.e., lens-shaped).