Outer teeth below sign of storm (7)

I believe the answer is:

thunder

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

'sign of storm' is the definition.
'thunder' can be an answer for 'storm' (thesaurus). I am not certain of the 'sign of' bit.

'outer teeth below' is the wordplay.
'outer' means to remove the middle letters.
'below' becomes 'under' (synonyms).
'teeth' with its centre taken out is 'th'.
'th'+'under'='THUNDER'

Can you help me to learn more?

(Other definitions for thunder that I've seen before include "Heavenly claps?" , "Weather featuring with 1" , "Deep rumbling sound" , "Rumble after lightning" , "It accompanies lightning" .)

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

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