How to make out 'Have it in for'?

[Haihao]

Hi,

Can anyone explain for me the following phrase:?

I understand that 'He has it in for me' = 'He dislikes me'.
What is the 'it' for? and why can the combination come to mean 'dislike'?

Thank you very much in advance. haihao

[Canadian45]

"have it in for someone" is an idiom. Besides disliking you, the person may also try to cause you some trouble or harm.

"it" has no specific meaning that I know of; "it" is just part of the idiom, like "has" and "in" are.

[Ron1970]

"Have it in for" implies that the subject has a (take your pick):

grudge
bitterness
resentment

"it" IMO represents these feelings.