To swim under water.
To jump into water head-first.
To jump headfirst toward the ground or into another substance.
to dive into home plate
To descend sharply or steeply.
(especially with in) To undertake with enthusiasm.
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.