one-to-one

adjective
1
between two people only
فرد به فرد, منحصراً با حضور دو نفر, دو نفره
2
matching something else in an exact way
یک‌به‌یک, تک‌به‌تک
There is no one-to-one correspondence between sounds and letters.
adverb
1
with only two people involved
یک به یک, رو در رو, دونفره