The pair Cleo possibly holds up (6)
I believe the answer is:
couple
'the pair' is the definition.
(couple is a kind of pair)
'cleo possibly holds up' is the wordplay.
'possibly' indicates anagramming the letters.
'holds' means one lot of letters goes inside another.
'cleo' anagrammed gives 'cole'.
'cole' enclosing 'up' is 'COUPLE'.
(Other definitions for couple that I've seen before include "Pair of attached people" , "Duo, brace" , "Two - join up" , "The pair to join together" , "Twosome" .)