Body cavity studied by top scientists in America (5)
I believe the answer is:
sinus
'body cavity' is the definition.
(sinus is a kind of body cavity)
'top scientists in america' is the wordplay.
'top' suggests taking the first letters.
'america' becomes 'US' (United States).
The first letter of 'scientists' is 's'.
's'+'in'+'us'='SINUS'
'studied by' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for sinus that I've seen before include "chamber" , "Hollow space" , "Bodily cavity" , "Cavity in body (connecting to nose)" , "Cavity linked to nose" .)