I. du‧et¹ /djuˈet $ duˈet/ noun [countable]
[Date: 1700-1800; Language: Italian; Origin: duetto, from duo 'group of two']
a piece of music for two singers or players ⇒ quartet, solo, trio

[TahlilGaran] Dictionary of Contemporary English ▲

II. duet² verb (past tense duetted, past participle duetting)
if one singer or musician duets with another, they sing or play together

[TahlilGaran] Dictionary of Contemporary English ▲

pair two things of the same type that you use together. Also used about two people who do something together or who you often see together:
a pair of shoes
a pair of socks
Winners will receive a pair of tickets for the show.
The pair were arrested six days after the killing.
They're a funny pair!
The British pair will be playing in the final on Saturday.
a couple (of something) two things of the same type, or a very small number of things:
There were a couple of empty seats at the table.
Do you have any stamps? I just need a couple.
couple noun [countable] two people who are married or having a sexual relationship:
a married couple
The couple met at university.
twins noun [plural] two children who were born on the same day to the same mother:
The twins look very alike.
identical twins
duo noun [countable] two people who perform together or who are often seen together:
a comedy duo
duet noun [countable] a piece of music written for two people to play:
They played a duet by Brahms.
twice two times adverb:
The group meets twice a week.
She sneezed twice.
for two for two people:
A table for two, please.
double bed/double room a bed for two people, or a room that has a bed for two people in it:
I'd like to book a double room.
twin beds/twin room two separate single beds, or a room with two separate single beds:
We asked for a twin room, and they've give us a double room.

[TahlilGaran] English Thesaurus ▲