Visible part of an iceberg (3)
I believe the answer is:
tip
'visible part of an iceberg' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tip that I've seen before include "End - pourboire" , "single piece of asparagus, perhaps" , "Point of gratuity" , "Empty" , "List, gratuity" .)