Definition of internal combustion in US English:

internal combustion

noun

  • 1Combustion (in early use especially spontaneous combustion) occurring or supposed to occur within something; specifically the metabolic process by which heat is generated in the animal body.

  • 2Combustion of petrol, oil, or other fuel within a closed space inside an engine, with the hot gases produced driving a piston or doing other work inside that space; frequently attributive, especially in "internal combustion engine".

Origin

Late 18th century; earliest use found in William Hutchinson (1732–1814), topographer. From internal + combustion.

Pronunciation

internal combustion

/ɪnˌtəːnl kəmˈbʌstʃ(ə)n/