Very sick beginning to 'Animal House' (5)
I believe the answer is:
villa
'house' is the definition.
(villa is a kind of house)
'very sick beginning to animal' is the wordplay.
'very' becomes 'v' (abbreviation).
'sick' becomes 'ill' (similar in meaning).
'beginning to' indicates taking the first letters.
The initial letter of 'animal' is 'a'.
'v'+'ill'+'a'='VILLA'
(Other definitions for villa that I've seen before include "Classical country house" , "Holiday residence" , "Roman domicile" , "Country house (in Aston?)" , "Roman or suburban house" .)