The Spanish initially suffered defeat (4)
I believe the answer is:
loss
'defeat' is the definition.
(thesaurus)
'the spanish initially suffered' is the wordplay.
'the spanish' becomes 'los' ('the' in Spanish**).
'initially' indicates taking the first letters.
The initial letter of 'suffered' is 's'.
'los'+'s'='LOSS'
(Other definitions for loss that I've seen before include "Defeat; bereavement" , "Bandleader" , "(Sports) defeat" , "Destruction" , "Financial reverse" .)