Lack of variety cycling — correct? Let me think! (6)
I believe the answer is:
tedium
'lack of variety' is the definition.
(I've seen this in another clue)
'correct? let me think' is the wordplay.
'correct?' becomes 'tedi' (I can't justify this - if you can you should give a lot more credence to this answer).
'let me think' becomes 'um' (expression of hesitation).
'tedi'+'um'='TEDIUM'
'cycling' acts as a link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for tedium that I've seen before include "Boredom, tiresomeness" , "Routine" , "'Boredom, ennui (6)'" , "Banality" , "Boredom with monotony" .)