put (one) under
To render unconscious by anesthesia, as during a surgical procedure. Your daughter is doing great. We put her under with no issues, and the surgeon is operating now. I've never had surgery before, and I'm really nervous for when they put me under—what if I don't wake up?
put someone or something under something
to place someone or something beneath something. Dave put Sam under the loft in the barn, hoping no one would find him there. Alice put the birthday present under the couch, where she could get to it in a hurry.
put someone under
Fig. to anesthetize someone. They put him under with ether. After you put her under, we will begin the operation.