Show off extremely frail relative (6)
I believe the answer is:
flaunt
'show off' is the definition.
(I know that show off can be written as flaunt)
'extremely frail relative' is the wordplay.
'extremely' says to hollow out the word (remove centre letters) (only the extremes of the word are used).
'relative' becomes 'aunt' (aunt is a type of relative).
'frail' with its middle taken out is 'fl'.
'fl'+'aunt'='FLAUNT'
(Other definitions for flaunt that I've seen before include "What's displayed in Globe" , "wave" , "Expose ostentatiously" , "Display ostentatiously, brandish" , "Show off, brandish" .)