Unlucky head in arrears makes first appearance (5)
I believe the answer is:
debut
'first appearance' is the definition.
(synonyms)
'unlucky head in arrears' is the wordplay.
'head' indicates taking the first letters.
'in' is an insertion indicator.
'arrears' becomes 'debt' (I've seen this before).
The initial letter of 'unlucky' is 'u'.
'u' put into 'debt' is 'DEBUT'.
'makes' acts as a link.
(Other definitions for debut that I've seen before include "Initial appearance" , "Aurora" , "where one began" , "First appearance, a coming-out" , "First appearance in society" .)