[From Bruce Nevin (2001.01.21 22:37 EST)]
Prescission is an action noun derived from the verb prescind; the latter is in Webster's. It is not related to prescient, etc. (science), but rather to excise, scissors, etc. OED says the verb is rare, and gives the main definitions thus:
1. to cut off beforehand, prematurely, or abruptly; to cut away or remove at once.
2. to cut off, detach, or separate from; to abstract
3. (intr. or refl. w/ from) to withdraw the attention from, to leave out of consideration