Hebrew, to the Spanish, is a treasure (5)
I believe the answer is:
jewel
'a treasure' is the definition.
(jewel is a kind of treasure)
'hebrew to the spanish' is the wordplay.
'hebrew' becomes 'Jew' (synonyms).
'to the spanish' becomes 'el' ('the' in Spanish).
'jew'+'el'='JEWEL'
'is' acts as a link.
(Other definitions for jewel that I've seen before include "(Semi) precious stone" , "Precious stone or mineral" , "Gemstone" , "The - That Was Ours (Dexter)" , "eg Ruby" .)