drop in

/D R AA1 P IH0 N/
verb
  1. 1

    (idiomatic) To arrive casually and unannounced, with little or no warning; also, to visit without an appointment.

  2. 2

    (surfing, intransitive) To paddle into and take off on a wave another surfer is already riding.

  3. 3

    (transitive, US) To install components, particularly car engines.

  4. 4

    (intransitive) To fall in; to cave in.

  5. 5

    Used other than figuratively or idiomatically: see drop, in.