He was putty thickset, round the shoulders, but he slimmed down towards his legs, and he stood about six feet high.
1650s, "thin, slight, slender," from Dutch slim "bad, sly, clever," from Middle Dutch slim "bad, crooked," from Proto-Germanic *slembaz "oblique, crooked" (cf. Middle High German slimp "slanting, awry," German schlimm "bad, cunning, unwell"). In English 17c. also sometimes with a sense "sly, cunning, crafty." Related: Slimly; slimness. With obsolete extended adjectival forms Slimsy "flimsy, unsubstantial" (1845); slimikin "small and slender" (1745). Slim Jim attested from 1887 in sense of "very thin person;" from 1902 as a type of slender cigar; from 1975 as a brand of meat snack.
To make neat and more attractive; furbish; gussy up: What are they all slicked up for? (1828+)