Frenchman worked longer, getting cross (7)
I believe the answer is:
mongrel
'cross' is the definition.
(I've seen this in another clue)
'frenchman worked longer getting' is the wordplay.
'frenchman' becomes 'm' (abbreviation for Monsieur - like 'Mr').
'worked' is an anagram indicator.
'getting' indicates putting letters inside.
'longer' anagrammed gives 'ongrel'.
'm' put into 'ongrel' is 'MONGREL'.
(Other definitions for mongrel that I've seen before include "Hybrid" , "mixed stock" , "of unknown variety" , "Cur" , "of mixed blood" .)