I wanted to deck him.
This is an informal use of the word, meaning to knock someone to the ground with a punch. (Possibly coming from fighting among sailors, where the 'floor' would actually be the deck of the ship.)
The formal use of the word 'to deck' means 'to decorate or adorn brightly or festively' ( as in the Christmas carol Deck the Halls with Boughs of Holly)
'to deck out' and 'to be decked out' means that one has put on one's best clothes for some occasion. "He was all decked out for his first date with a girl he'd met." (In effect, one has 'decorated' oneself up to look good!)