Unfortunately, partner's tan is see-through (11)
I believe the answer is:
transparent
'see-through' is the definition.
('transparent' can be a synonym of 'see-through')
'unfortunately partner's tan' is the wordplay.
'unfortunately' is an anagram indicator.
'partners'+'tan'='partnerstan'
'partnerstan' with letters rearranged gives 'TRANSPARENT'.
'is' acts as a link.
(Other definitions for transparent that I've seen before include "Obvious - ingenuous" , "Lucid - evident - clear" , "Frank" , "poor at lying" , "Open" .)