Mum cut short by American, jolly old satyr (7)

I believe the answer is:

silenus

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'jolly old satyr' is the definition.
'silenus' can be an answer for 'satyr' (thesaurus). I am unsure of the 'jolly old' bit.

'mum cut short by american' is the wordplay.
'mum' becomes 'silent' (to keep mum can informally mean to stay silent).
'cut short' means to remove the last letter.
'by american' becomes 'us' (abbreviation for United States. I am not sure about the 'by' bit.).
'silent' with its final letter removed is 'silen'.
'silen'+'us'='SILENUS'

Can you help me to learn more?

(Other definitions for silenus that I've seen before include "Greek deity" , "god" .)

I've seen this clue in The Telegraph.

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