Puzzle over German scaling snowcap (5)

I believe the answer is:

rebus

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

'puzzle' is the definition.
(type of visual puzzle)

'over german scaling snowcap' is the wordplay.
'over' becomes 're'.
'german scaling snowcap' becomes 'bus' (I can't justify this - if you can you should give a lot more credence to this answer).
're'+'bus'='REBUS'

Can you help me to learn more?

(Other definitions for rebus that I've seen before include "Visual pun" , "Visual type of word puzzle" , "Pun picture puzzle" , "Visual wordplay - Rankin's inspector" , "solver?" .)

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

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