"Absolutely simian!" and an exclamation of impatience (5)

I believe the answer is:

apish

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'absolutely simian' is the definition.
'apish' can be an answer for 'simian' (I've seen this in another clue). I'm not sure about the 'absolutely' bit.

'an exclamation of impatience' is the wordplay.
'an' becomes 'a'.
'exclamation of impatience' becomes 'pish' (I can't justify this - if you can you should believe this answer much more).
'a'+'pish'='APISH'

'and' acts as a link.

Can you help me to learn more?

(Other definitions for apish that I've seen before include "Foolish; simian" , "Silly" , "Foolish; like a monkey" , "Stupid" , "Foppish" .)

I've seen this clue in the Evening Standard.

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