4-6-4

plural 4-6-4s

1. Under the Whyte notation system, a steam locomotive that has four leading wheels arranged in a leading truck, six coupled driving wheels and four trailing wheels in a trailing truck.

   Most Canadian engines are black. [...] The C.N.R. has only three classes of non-black engines, the "6400s", the later 4-8-2s and the 4-6-4s.

   1959 November 28, J. N. Westwood, “The Railways of Canada”, in Trains Illustrated, page 552

   1 more example

   No sooner had a waiting locomotive backed on to its train, the vociferous 4-6-4 or 4-8-4 re-emerged from under the bridge, and the two red marker lights on the last vehicles passed, than the headlight of the electric engine hauling the following train could be seen under the bridge and the waiting queue of locomotives had moved up one.

   1954 January 28, H. P. White, “Vignettes of the Rail”, in Railway Magazine, page 54, at Harmon station, New York