Imagine flimsy silk finish! (5)
I believe the answer is:
think
'imagine' is the definition.
('think' can be a synonym of 'imagine')
'flimsy silk finish' is the wordplay.
'flimsy' becomes 'thin' ('thin' can be similar in meaning to 'flimsy').
'finish' suggests the final letters.
The last letter of 'silk' is 'k'.
'thin'+'k'='THINK'
(Other definitions for think that I've seen before include "Judge, consider" , "Believe" , "Ponder" , "figure" , "Use one's mind" .)