Found in the following dictionaries
OTCWL2014 (NASPA Word List 2014)
"Headbutt" Definition
noun
A sharp blow delivered by driving the head into the opponent, generally by lowering the head and charging forward or by rapidly tilting the head backward and then forward.
Source: Wiktionary
verb
To deliver a sharp blow by driving the head into an opponent.
Source: Wiktionary
Butt with the head.
Source: Wordnet
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