Sheik oddly neglected to call about the Spanish mercenary (8)
I believe the answer is:
hireling
'mercenary' is the definition.
(thesaurus)
'sheik oddly neglected to call about the spanish' is the wordplay.
'oddly neglected' indicates alternate letters.
'to call' becomes 'ring' ('ring' can be a synonym of 'call'**).
'about' means one lot of letters goes inside another.
'the spanish' becomes 'el'.
The alternating letters of 'sheik' are 'hi'.
'ring' going around 'el' is 'reling'.
'hi'+'reling'='HIRELING'
(Other definitions for hireling that I've seen before include "Mercenary worker" , "Menial worker" , "Minor employee" , "Person working for money" , "One's got engaged" .)