1) Cookbook word 2) First verb in many recipes 3) First word in many recipes 4) Get the oven ready 5) Heat 6) Heat beforehand 7) Heat up 8) Oven-baking instruction 9) Prepare for baking 10) Prepare the oven 11) Recipe verb 12) Warm beforehand 13) Warm early 14) Warm up an oven 15) Warm up before cooking 
To set an oven or broiler at the desired temperature 15 to 30 minutes before use so that the temperature is reached before food is put in to cook.
The preheating stage of a process, especially for wave soldering or reflow soldering. 
To heat the oven, grill or toaster to a desired temperature before inserting the food.
[v] - heat beforehand
To set the oven or grill to a specific temperature to allow the internal temperature to increase sufficiently before cooking.
Turning the oven/pan beforehand to let it come to the desired temperature.
to heat the oven before baking. Always fully preheat the oven at least 15 minutes before baking.
Very important in baking. Heat the oven, griddle, skillet or broiler to the desired temperature before inserting the food. TIP: Always check the oven to be sure nothing is in it—and place the oven racks in the correct position before preheating. 
to heat before using or before subjecting to some further process: to preheat an oven before baking a cake.