(A). One engaged in delivering and loading ships' cargoes.
“Judging of my histrionic powers by my outward man, he probably thought me more flt for a dock-side lumper than an actor.” —C. Thomson: Autobiography, p. 191.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on Dock-side Lumper from Infoplease: