tank engine

tank engine (plural tank engines)

1. a type of steam locomotive train which carries its own fuel and water in the same unit, and so does not pull a tender

   Cuthbert Hamilton Ellis, The Beauty of Old Trains (1952) p. 117:

   • The 2-4-2 tank engines of the Great Eastern and the London and North Western were simply adaptations of 2-4-0 main-line engines; the 0-4-4 tank engine owed its parentage to the archaic 0-4-2 mixed traffic.