Swimmer admits dirty look and gesture (8)
I believe the answer is:
flourish
'gesture' is the definition.
(flourish is a kind of gesture)
'swimmer admits dirty look' is the wordplay.
I cannot really see how this works, but
'look' could be 'lo' (archaic term meaning 'look!') and 'lo' is found in the answer.
This may be the basis of clue (or it may be nonsense).
'and' acts as a link.
Can you help me to learn more?
(Other definitions for flourish that I've seen before include "Thrive; ornamental passage of music" , "Prosper - display" , "Wax" , "Grow vigorously and healthily" , "success" .)