Headfirst Plunge is a phrase that describes the act of diving into something without hesitation or preparation. It is often used to describe someone who dives into a situation without thinking it through or considering the consequences. The term can also be used to describe someone who takes a risk without considering the potential risks or rewards. The crossword solution for this term is 'DIVE, ' which is a four-letter word that describes the action of jumping into water headfirst.