Headache for Frenchman travelling Nigeria (8)
I believe the answer is:
migraine
'headache' is the definition.
(migraine is a kind of headache)
'frenchman travelling nigeria' is the wordplay.
'frenchman' becomes 'm' (abbreviation for Monsieur - like 'Mr').
'travelling' indicates anagramming the letters.
'nigeria' with letters rearranged gives 'igraine'.
'm'+'igraine'='MIGRAINE'
'for' is the link.
(Other definitions for migraine that I've seen before include "terrible pain" , "A really bad headache" , "may give one a sort of headache" , "Intense headache" , "Recurrent throbbing headache" .)