Ref nuts to wave card? (7)

I believe the answer is:

funster

I'm a little stuck... Click here to teach me more about this clue!

'wave card?' is the definition.
The definition suggests a singular noun which matches the answer.

'ref nuts' is the wordplay.
'ref nuts' anagrams to 'FUNSTER'.
However, I'm not clear how this is indicated.

'to' acts as a link.

Can you help me to learn more?

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