Incomparable lady enthralling all at last (8)
I believe the answer is:
peerless
'incomparable' is the definition.
(similar in meaning)
'lady enthralling all at last' is the wordplay.
'lady' becomes 'peeress' (female peer).
'enthralling' indicates putting letters inside.
'at last' says to take the final letters.
The last letter of 'all' is 'l'.
'peeress' going around 'l' is 'PEERLESS'.
(Other definitions for peerless that I've seen before include "Excellent" , "Unequalled" , "Unique" , "Unmatched" , "Outstanding" .)