Definitions for half nelson
Random House Webster's College Dictionary
a hold in which a wrestler, from behind the opponent, passes one arm under the corresponding arm of the opponent and locks the hand on the back of the opponent's neck.
Ref: Compare full nelson.
a wrestling hold in which the holder puts an arm under the opponent's arm and exerts pressure on the back of the neck
A hold in which the wrestler applying the hold puts one arm under the arm of their opponent and applies pressure to the back of their opponents head or neck.