Crossword Genius

Declared whopper croc’s cousin a menace to motorists (9)

Ross

I believe the answer is:

tailgater

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

'cousin a menace to motorists' is the definition.
I can't judge whether this defines the answer.

'declared whopper croc's' is the wordplay.
'declared' indicates a 'sounds like' (homophone) clue.
'whopper' becomes 'tale' (I've seen this in another clue).
'croc's' becomes 'gater' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'tale' sounds like 'tail'.
'tail'+'gater'='TAILGATER'

Can you help me to learn more?

(Another definition for tailgater that I've seen is " One closely follows".)

I've seen this clue in the Sydney Morning Herald.
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