Tell son to go to mountain (5)

I believe the answer is:

speak

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'tell son' is the definition.
'speak' can be an answer for 'tell' (thesaurus). I am not sure about the 'son' bit.

'go to mountain' is the wordplay.
'go to' becomes 's' (I am not sure about this - if you are sure you should believe this answer much more).
'mountain' becomes 'peak' (I've seen this before).
's'+'peak'='SPEAK'

'to' is the link.

Can you help me to learn more?

(Other definitions for speak that I've seen before include "Utter words" , "Converse" , "Talk" , "give a lecture" , "express" .)

I've seen this clue in The Telegraph.

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