Meticulous, firm, Everyman had promises to pay later (10)
I believe the answer is:
fastidious
'meticulous' is the definition.
(similar in meaning)
'firm everyman had promises to pay later' is the wordplay.
'firm' becomes 'fast' (synonyms).
'everyman had' becomes 'I'd' (where the crossword setter is 'Everyman').
'promises to pay' becomes 'IOU's' (promises to pay a debt).
'later' is a charade indicator (letters next to each other).
'fast'+'id'+'ious'='FASTIDIOUS'
(Other definitions for fastidious that I've seen before include "Attentive to detail" , "Meticulous" .)