Webster's Revised Unabridged Dictionary · 1913

Sitfast

Sitfast , adjective

[Sit + fast.]

Fixed; stationary; immovable. [Rare]
'T is good, when you have crossed the sea and back, To find the sitfast acres where you left them. — Emerson

Sitfast , noun

(Farriery) A callosity with inflamed edges, on the back of a horse, under the saddle.