Frank rants about relative (11)
I believe the answer is:
transparent
'frank' is the definition.
(I've seen this before)
'rants about relative' is the wordplay.
'about' indicates an anagram.
'relative' becomes 'parent' (parent is a kind of relative**).
'rants' with letters rearranged gives 'trans'.
'trans'+'parent'='TRANSPARENT'
(Other definitions for transparent that I've seen before include "Open" , "unmistakable" , "poor at lying" , "Lucid - evident - clear" , "Obvious - ingenuous" .)