'postcatechumenal' originates from Latin and Greek elements, specifically the Latin prefix 'post-' (from Latin 'post' meaning 'after') combined with 'catechumenal', which ultimately traces to Greek 'katechoumenos' (κατηχούμενος), where 'katechoumenos' meant 'one being instructed (in the catechesis)'.

'postcatechumenal' developed as a Modern English formation combining 'post-' + Middle/Medieval Latin and Late Latin forms related to 'catechumen' (from Greek 'katechoumenos'); Medieval Latin usages such as 'catechumenatus' and adjectival forms produced English 'catechumenal', to which the prefix 'post-' was added in modern usage to form 'postcatechumenal'.

Initially it referred specifically to things 'after the catechumenate' (the instruction period before baptism); over time it has retained this core sense and is used chiefly in theological and historical contexts to denote the period or matters occurring after catechetical instruction.