4-6-6-2 Definition

noun

Under the Whyte notation system, a Mallet-type locomotive with four leading wheels on a leading truck, two sets of six driving wheels, and two trailing wheels on a trailing truck.

Wiktionary

Under the Whyte notation system, a Mallet-type locomotive with four leading wheels on a leading truck, two sets of six driving wheels, and four trailing wheels on a trailing truck.

Wiktionary