Notice blade and fluctuate (6)
I believe the answer is:
seesaw
'fluctuate' is the definition.
(I've seen this before)
'notice blade' is the wordplay.
'notice' becomes 'see' (notice can mean to spot or see).
'blade' becomes 'saw' (I can't justify this - if you can you should give a lot more credence to this answer).
'see'+'saw'='SEESAW'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for seesaw that I've seen before include "Plaything with up-and-down movement" , "Go one way and then the other" , "swing" , "Child's game with plank on barrel" , "Children's playground item" .)