'contain' originates from Latin, specifically the word 'continere', where 'con-' meant 'together' and 'tenere' (or 'tenēre') meant 'to hold'.

'contain' changed from Latin 'continere' to Old French 'contenir' (or Anglo-French forms) and entered Middle English as 'containen'/'containen' before becoming the modern English 'contain'.

Initially it meant 'to hold together' or 'to restrain/hold', and over time it evolved into the modern sense 'to hold within' or 'to include' (and extended metaphorically to 'restrain emotions').