It stimulates high speed, I see (5)

I believe the answer is:

tonic

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'it stimulates high' is the definition.
The definition suggests a singular noun which matches the answer.

'speed i see' is the wordplay.
'speed' becomes 'ton' (I've seen this before).
'see' becomes 'C' (the word for the letter, according to Chambers).
'ton'+'i'+'c'='TONIC'

Can you help me to learn more?

(Other definitions for tonic that I've seen before include "shot in the arm" , "Quinine water" , "Important note" , "Stimulant" , "that may be mixed with gin" .)

I've seen this clue in the Evening Standard.

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