A Deux Definition

ä dœ
adjective
Of or involving two individuals, especially when of a private or intimate nature.
American Heritage

Of, for, or involving only two people; one-on-one.

"It is arguable that Litvinov, had he met with civility and those supple conversations à deux in which trained diplomats excel, might have stopped the war..." --William Manchester, The Last Lion Vol. 2, page 458
Wiktionary
adverb
Privately with only two individuals involved.
Dining à deux.
American Heritage
Of or for two.
Webster's New World
Intimate(ly)
Webster's New World
Wiktionary