|enquire / enquiry
inquire / inquiry
|In British English there's a subtle difference between enquiry and inquiry, but Americans tend to use inquiry for both, as a result the lines are getting blurred, but generally:-
If you enquire about someone or something you ask about them.
She enquired about his health. He was touched by her enquiry..
In British English we use inquiry when we're talking about more official investigations.
She thought the committee had no right to inquire into her politics.
!Note - If you can't decide, stick to inquire / inquiry. You'll sound like an American, but that can't be helped.