Lewis & Short

spissĭtūdo, ĭnis, f. [spissus], thickness, density, consistency (post-Aug. and very rare): aëris crassi, Sen. Q. N. 2, 30, 4: mellis, Scrib. Comp. 4; 5: emplastri, id. ib. 81: non nimis liquida, id. ib. 37: spissitudinem ejus absolvere, Pall. 12, 17, 2.