Impressive meow as Siamese finally stirs (7)
I believe the answer is:
awesome
'impressive' is the definition.
(similar in meaning)
'meow as siamese finally stirs' is the wordplay.
'finally' says to take the final letters.
'stirs' indicates an anagram.
The last letter of 'siamese' is 'e'.
'meow'+'as'+'e'='meowase'
'meowase' anagrammed gives 'AWESOME'.
(Other definitions for awesome that I've seen before include "Stupendous" , "Simultaneously wonderful" , "Exceptionally good" , "Hugely impressive, creating fear and wonder" , "Daunting" .)