The most common and most likely answer to this crossword clue is the 3 plus 6 letter word SEE DOUBLE
I've seen this crossword clue in Independent
S
E
E
D
O
U
B
L
E
More clues leading to the result SEE DOUBLE
- Date twin? One might after blow to head
- Get large drink – and experience its effect?
- Two options for gambler to make pair out of singleton?
- Experience an illusion having date with a large drink
- Date twin and experience an illusion
- Have 8/22 vision?
- Notice Doppelganger's sight is under influence of alcohol
- Understand whisky perhaps could make one this
Buddy explains!

The straight part
We know that "to make pair out of singleton?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case to make pair out of singleton? = see double.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.