'custard-apple' is a compound of the English words 'custard' and 'apple'; 'custard' entered English from Middle English/Anglo-Norman 'croustade'/'crustade' (Old French), originally a tart or pie with a crust and later the creamy filling of such tarts, while 'apple' comes from Old English 'æppel' meaning 'fruit'.

'custard' developed in Middle English from Old French/Anglo-Norman terms for a crusted dish and shifted to mean the egg-and-cream filling; 'apple' retained the older sense of a fruit. The compound 'custard-apple' arose in early modern English as a descriptive name for fruits with a soft, custard-like flesh that roughly resembled an 'apple' in being a singular fruit.

Initially the elements referred to a custard-like filling and a generic fruit ('apple'); over time the compound came to be used specifically for certain tropical Annona fruits whose flesh resembles custard, so the modern meaning is the particular fruit/tree rather than a literal 'custard' or 'apple.'