Sounds like a pretty girl who's taking the plunge! (6,4)
I believe the answer is:
diving bell
'the plunge' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'sounds like a pretty girl who's' is the wordplay.
I cannot quite see how this works, but
'girl' could be 'bell' and 'bell' is found within the answer.
The remaining letters 'diving' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'taking' is the link.
Can you help me to learn more?
(Other definitions for diving bell that I've seen before include "Sea-bottom work chamber supplied air by tube" , "It lowers one in the main" .)