Entry 2 senses · 2 variants Webster, 1913 Sitfast · Sit·fast · IPA a. n. 01 a. Fixed; stationary; immovable. 1. Fixed; stationary; immovable.[R.] “'T is good, when you have crossed the sea and back, To find the sitfast acres where you left them.” — Emerson. 02 n. A callosity with inflamed edges, on the back of a horse, under the saddle. 1. A callosity with inflamed edges, on the back of a horse, under the saddle.(Far.)