'unequal-cotyledonous' originates from modern English, composed of 'unequal' and 'cotyledonous'. 'unequal' comes from Old English/Old French roots combining the negative prefix 'un-' with 'equal' (from Latin 'aequālis'), and 'cotyledonous' derives from 'cotyledon' (from Greek 'kotyledon'), with the adjectival suffix '-ous'.

'cotyledon' comes from Greek 'kotyledon' (κοτύληδον), adopted into Latin and later into botanical Latin and English as 'cotyledon'; the adjective 'cotyledonous' was formed in English with the suffix '-ous', and the compound descriptive phrase 'unequal-cotyledonous' developed in botanical usage to describe seedlings with unequal cotyledons.

Initially the root 'cotyledon' referred to a cup-shaped hollow (from Greek), and in botanical use it came to mean 'seed leaf'; combined with 'unequal' the compound has consistently meant 'having unequal seed leaves' and has retained that specific botanical meaning.