'ateleiosis' originates from Greek, specifically the word 'ateleíōsis' (ἀτελειωσις), where the prefix 'a-' meant 'not' and 'teleiosis'/'teleios' meant 'complete' or 'perfect'.

'ateleiosis' entered English via modern scholarly/medical/philological usage from Greek (sometimes through Latinized forms) and has been used in English texts since the 19th century in specialized contexts.

Initially it meant 'lack of completion' in the literal Greek sense, and over time it has retained this core meaning, used chiefly in technical, rhetorical, or literary contexts to denote incompleteness.