'pro-merger' is a modern compound formed from the prefix 'pro-' and the noun 'merger'. 'pro-' originates from Latin 'pro' meaning 'for' or 'in favor of', and 'merger' derives from the verb 'merge' plus the agent/nominalizing suffix '-er'.

'merger' comes from the verb 'merge', which traces back to Latin 'mergere' meaning 'to plunge' or 'to dip'. The sense shifted via Medieval and later usage to mean 'to combine' or 'unite', producing the corporate noun 'merger'. The productive prefix 'pro-' (Latin 'pro') was later attached in English to indicate support, yielding compounds like 'pro-merger' in corporate and political discourse in the 20th century.

Originally Latin 'mergere' meant 'to plunge or sink'; over time the sense broadened to 'to join or combine', and 'merger' came to mean the joining of organizations. 'Pro-merger' specifically developed to mean 'in favor of such a joining'.