The first of the postmen with unusually clear package (6)
I believe the answer is:
parcel
'package' is the definition.
(I know that package can be written as parcel)
'the first of the postmen with unusually clear' is the wordplay.
'the first of' says to take the initial letters.
'with' is a charade indicator (letters next to each other).
'unusually' indicates anagramming the letters.
The first letter of 'postmen' is 'p'.
'clear' anagrammed gives 'arcel'.
'p'+'arcel'='PARCEL'
(Other definitions for parcel that I've seen before include "Package wrapped in paper" , "Small piece of land" , "Packet" , "Amount of land; package" , "Piece (of land); something to post" .)