... Truss initially going on record with papers lacking enthusiasm (5)
I believe the answer is:
tepid
'lacking enthusiasm' is the definition.
(I've seen this before)
'truss initially going on record with papers' is the wordplay.
'initially' indicates taking the first letters.
'going on' says to put letters next to each other.
'record' becomes 'ep' (abbreviation for extended play record).
'with' means one lot of letters go next to another.
'papers' becomes 'ID' (identifying documents are one's 'papers').
The initial letter of 'truss' is 't'.
't'+'ep'+'id'='TEPID'
(Other definitions for tepid that I've seen before include "Warmish" , "Unenthusiastic - cool" , "without passion" , "Showing little interest or enthusiasm" , "without enthusiasm" .)