'heat-treater' originates from English as a compound of 'heat' + 'treat' with the agentive suffix '-er'. 'Heat' comes from Old English 'hǣtu' meaning 'heat, warmth', and 'treat' comes from Old French 'traiter' (from Latin 'tractare') meaning 'to handle or deal with'. The suffix '-er' forms an agent noun meaning 'one who performs the action'.

'heat' developed from Old English 'hǣtu' and Proto-Germanic roots; 'treat' passed into English via Old French 'traiter' from Latin 'tractare'. The compound 'heat-treater' is a modern English formation combining these elements with '-er' to denote an agent, and the plural 'heat-treaters' follows regular English pluralization.

Initially the components referred simply to 'heat' and 'to handle/deal with'. Over time, the compound came to specifically denote 'one who applies heat as a treatment', a meaning that is retained in modern technical usage.