'pro-vivisectionist' is formed from the prefix 'pro-' (from Latin 'pro', meaning 'for') combined with 'vivisectionist' (built from 'vivisection' + the agent suffix '-ist'). 'Vivisection' itself ultimately comes from Latin elements 'vivus' meaning 'living' and 'sectio' (from 'secare') meaning 'a cutting.'

'Vivisection' entered English via French 'vivisection' in the 19th century (literally 'cutting the living'); the agent-forming suffix '-ist' produced 'vivisectionist', and the prefix 'pro-' was later attached to denote someone 'for' that practice, yielding 'pro-vivisectionist'.

Initially, 'vivisection' meant 'cutting of the living' (literal surgical cutting of living organisms); over time it came to refer more broadly to experimental surgery or experimentation on live animals. 'Pro-vivisectionist' now denotes someone who supports that practice.