E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A contraction of navigator. One employed to make railways.
Canals were thought of as lines of inland navigation and a tavern built by the side of a canal was called a Navigation Inn. Hence it happened that the men employed in exoavating canals were called navigators, shortened into navvies.Spencer: Principles of Sociology, vol. i. appendix C, p. 834.