Combustion

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late Middle English: from late Latin combustio(n- ), from Latin comburere ‘burn up’.

wiktionary

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From Old French combustion, from Latin combustio, from comburere(“to burn”), itself from the intensifying prefix com- + the root burere (a faulty sep. of amburere "to burn around", itself from ambi- + urere "to burn, singe"); equivalent to combust +‎ -ion.

etymonline

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combustion (n.)

"action or process of burning," early 15c., from Old French combustion (13c.) and directly from Latin combustionem (nominative combustio) "a burning," noun of action from past-participle stem of Latin comburere "to burn up, consume," from com-, here perhaps an intensive prefix (see com-), + *burere, based on a faulty separation of amburere "to burn around," which is properly ambi-urere, from urere "to burn, singe" (from PIE root *heus- "to burn;" see ember).