Father beginning to show anger (4)
I believe the answer is:
sire
'father' is the definition.
(synonyms)
'beginning to show anger' is the wordplay.
'beginning to' says to take the initial letters.
'anger' becomes 'ire' (ire is intense rage).
The initial letter of 'show' is 's'.
's'+'ire'='SIRE'
(Other definitions for sire that I've seen before include "Bear" , "Male parent of a horse, for example" , "Stallion; beget" , "Rise for male parent (4)." , "Male parent of, say, horse" .)