2-2 Definition

noun

Under the Whyte notation system, a steam locomotive that has one unpowered leading axle and one powered driving axle.

Wiktionary
Under the Whyte notation system, a steam locomotive that has two leading wheels, two driving wheels and two trailing wheels.
Wiktionary
Under the Whyte notation system, a steam locomotive that has two leading wheels followed by two coupled driving wheels and four trailing wheels.
Wiktionary

Other Word Forms of 2-2

Noun

Singular:
2-2
Plural:
2-2-0s, 2-2-2s, 2-2-4s