Vessel in pond's capsizing (5)
I believe the answer is:
sloop
'vessel' is the definition.
(thesaurus)
'pond's capsizing' is the wordplay.
'pond's' becomes 'pools' ('pool' can be a synonym of 'pond').
'capsizing' shows that the letters should be reversed in order.
'pools' written backwards gives 'SLOOP'.
'in' acts as a link.
(Other definitions for sloop that I've seen before include "Sailing vessel with one mast" , "Vessel with a single mast" , "One-masted sailing boat" , "something that's rigged" , "One-masted sailing ship" .)