Adjectives

(s)man-to-manforthright and honest“had a man-to-man talk about the facts of life”
(s)one-on-one, man-to-manbeing a system of play in which an individual defensive player guards an individual offensive player“one-on-one defense”

Adverbs

(r)man-to-manstraightforwardly or frankly“we must talk man-to-man”