Like the clappers are striking: without end? (7)
I believe the answer is:
rapidly
'like the clappers' is the definition.
Both the answer and definition are adverbs.
Maybe they are linked in a way I don't understand?
'striking without end?' is the wordplay.
'striking' becomes 'rap' (rap is a kind of striking).
'without end?' becomes 'idly' (I can't justify this - if you can you should give a lot more credence to this answer).
'rap'+'idly'='RAPIDLY'
'are' is the link.
Can you help me to learn more?
(Other definitions for rapidly that I've seen before include "With great speed" , "Quickly" , "Speedily" , "At a great rate" , "right off the bat" .)