The most common and most likely answer to this crossword clue is the 4 letter word DYAD
I've seen this crossword clue in Independent
D
Y
A
D
More clues leading to the result DYAD
Buddy explains!

The straight part
We know that "Couple" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case couple = dyad.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 DYAD mean?
DYAD noun- A set of two elements treated as one; a pair.
- Any set of two different pitch classes.
- A pair of things standing in particular relation; dyadic relation.
- An element, atom, or radical having a valence or combining power of two.
- A secondary unit of organisation consisting of an aggregate of monads.
- A tensor of order two and rank one.