Pair, uneasy at first, entering function (3)
I believe the answer is:
duo
'pair' is the definition.
(two people)
'uneasy at first entering function' is the wordplay.
'at first' suggests taking the first letters.
'entering' is an insertion indicator.
'function' becomes 'do' (I've seen this in other clues).
The initial letter of 'uneasy' is 'u'.
'u' inserted inside 'do' is 'DUO'.
(Other definitions for duo that I've seen before include "They might play" , "Performing couple" , "Two-person act" , "Pair of singers" , "Pair of people/things" .)