'post-lunch' originates from Latin and English: specifically the Latin preposition 'post' (meaning 'after') combined with the English noun 'lunch' (from Middle English 'lunch(eon)'/ 'luncheon'), where 'post' meant 'after' and 'lunch' referred to a light meal.

'post' entered English via Latin 'post' (and through Old French influence) into Middle English as 'post-', while 'lunch' shortened from Middle English 'luncheon'/'lunch(eon)' to modern 'lunch'; these elements combined in modern English to form the compound 'post-lunch'.

Initially the elements meant 'after' + 'midday/light meal'; over time the compound came to be used specifically to describe events or times occurring after the midday meal (i.e., 'occurring after lunch').