E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Lump.
If you don’t like it, you may lump it. Whether you like to do it or not, no matter; it must be done. Here “lump it” means “to gulp it down,” or swallow unwillingly, to put up with it unwillingly but of necessity. Thus we say of medicine, “lump it down,” i.e. gulp it down. (Danish, gulpen, to swallow.)
