'appendicectasis' originates from a combination of Latin-derived 'appendix' (via New Latin) and Greek 'ektasis' (ἐκτασις), where 'ektasis' meant 'extension' or 'dilatation'.

'appendix' entered English from Latin 'appendix' (from 'appendere', meaning 'to hang on'), and 'ektasis' comes from Greek ἐκτασις. The medical formation '...ectasis' (as in 'bronchiectasis') has been productive in modern medical English to denote dilation, leading to formations such as 'appendicectasis'.

Initially the components meant 'something that hangs on' (appendix) and 'extension/dilatation' (ektasis); combined in modern medical usage they denote 'dilatation of the appendix'.