The most common and most likely answer to this crossword clue is the 3 letter word DUO
I've seen this crossword clue in The Times
D
U
O
More clues leading to the result DUO
- Couple regularly encountered in Douro
- Twosome united in act
- Pair half of duck with a whole one
- Performers discovered unknown operatic intros
- Somewhat assiduous pair of people
- Couple turning noisy, left out
- Report of outstanding au pair
- Couple retreating inside boudoir
- Entering party united couple
- Due to get picked up along with au pair
Buddy explains!

The straight part
We know that "Twosome" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case twosome = duo.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does DUO mean?
DUO noun- Two people who work or collaborate together as partners; especially, those who perform music together.
- Any pair of two people.
- Any cocktail consisting of a spirit and a liqueur.
- A song in two parts; a duet.