1.
In a one-to-one relationship, one person deals directly with only one other person.
...one-to-one training.
...negotiating on a one-to-one basis.
<i><i>ADJi>: <i>ADJi> <i>ni>i>
•
One-to-one is also an adverb.
She would like to talk to people one to one.
<i><i>ADVi>: <i>ADVi> after <i>vi>i>
2.
If there is a one-to-one match between two sets of things, each member of one set matches a member of the other set.
In English, there is not a consistent one-to-one match between each written symbol and each distinct spoken sound.
<i><i>ADJi>: <i>ADJi> <i>ni>i>