IPA: /priˈwɔːrmd/
KK: /priˈwɔrmd/
Warmed up before use or serving.
The prewarmed oven made baking the cake much easier.
Prewarmed is formed from "pre-" (meaning before) and "warm" (from Old English "wearm", meaning to make warm) and the suffix "-ed" (indicating a past action). The word "prewarmed" means to have been warmed beforehand.
Think of something being made warm "before" it is used — "pre-" means before, and "warm" means to heat.