Lewis & Short

crassĭfĭco, āvi, ātum, 1, v. a. [crassusfacio], to make thick, thicken, make fat, fatten, Cael. Aur. Tard. 2, 14, 208; 5, 2, 39 al.
Pass., to thicken, become dense, Cael. Aur. Tard. 2, 13, 180.