To swim under water.
To jump into water head-first.
To jump headfirst toward the ground or into another substance.
Example: "To dive into home plate"
To descend sharply or steeply.
(especially with in) to undertake with enthusiasm.
Example: "She dove right in and started making improvements."
To deliberately fall down after a challenge, imitating being fouled, in the hope of getting one's opponent penalised.
To cause to descend, dunk; to plunge something into water.
To explore by diving; to plunge into.
To plunge or to go deeply into any subject, question, business, etc.; to penetrate; to explore.
That or who dives or dive.