Almost transfix a type of antelope (6)
I believe the answer is:
impala
'type of antelope' is the definition.
(impala is a type of antelope)
'almost transfix a' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'transfix' becomes 'impale' (synonyms).
'impale' with its last letter taken off is 'impal'.
'impal'+'a'='IMPALA'
(Other definitions for impala that I've seen before include "horned beast" , "Breed of antelope" , "horny creature" , "African resident" , "Big game" .)