Fear Dad being visited by devil incarnate initially (6)
I believe the answer is:
phobia
'fear' is the definition.
(a phobia is a fear of a particular thing)
'dad being visited by devil incarnate initially' is the wordplay.
'dad' becomes 'pa' (both can mean one's father).
'being visited by' means one lot of letters goes inside another.
'devil' becomes 'hob' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'initially' says to take the initial letters.
The first letter of 'incarnate' is 'i'.
'hob'+'i'='hobi'
'pa' enclosing 'hobi' is 'PHOBIA'.
Can you help me to learn more?
(Other definitions for phobia that I've seen before include "Irrational fear of something" , "Obsessive and persistent fear of something" , "Overpowering fear" , "Morbid, irrational fear" , "An irrational fear or dislike" .)