'pro-taxation' is a compound built from the Latin prefix 'pro-' (from Latin 'pro' meaning 'for') and the noun 'taxation' (from Medieval Latin 'taxatio'), ultimately tracing to Latin 'taxare' meaning 'to estimate or assess'.

'taxare' in Latin developed into Medieval Latin 'taxatio' and Old French 'taxation', which entered Middle English as 'taxacioun' and later became modern English 'taxation'; the modern English prefix 'pro-' was then combined with 'taxation' to form 'pro-taxation' as a descriptive compound.

The original roots related to assessing or estimating (taxes); over time the compound came to be used as a political description meaning 'in favor of imposing taxes' or 'supporting taxation'.