Habit beginning to irritate an animal (5)
I believe the answer is:
coati
'an animal' is the definition.
(mammal of Central and South America)
'habit beginning to irritate' is the wordplay.
'habit' becomes 'coat' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'beginning to' indicates taking the first letters.
The initial letter of 'irritate' is 'i'.
'coat'+'i'='COATI'
Can you help me to learn more?
(Other definitions for coati that I've seen before include "carnivore from South America" , "wild animal" , "consumer of flesh" , "Raccoon-like animal of Central and S. America" , "South American animal" .)