Green’s Dictionary of Slang

1. a Navaho Indian.

1910		Z. Grey Heritage of Desert (1937) 10: Seen any Navvies?
1957		A. Bean Fancher Train 28: The Navvies are damn smart when it comes to breedin’ [HDAS].
1971		J.U. Terrell Bunkhouse Papers 184: They’re a no-good bunch of Navvies up around there [HDAS].

2. a Navaho pony.

1936		R.F. Adams Cowboy Lingo 86: The ‘navvy’ was a Navajo Indian pony, said to be about the poorest specimen of horse-flesh on earth.
1959		A. Sillitoe ‘Noah’s Ark’ Loneliness of the Long-Distance Runner (1960) 98: As though he were a tent from which ten buck-navvies were trying to escape.