Something we say is elusive or remains? (4,4)
I believe the answer is:
gold dust
'something we say is elusive' is the definition.
(gold dust can mean anything elusive or valuable)
'or remains?' is the wordplay.
'or' becomes 'gold' ('or' is the heraldic term for gold).
'remains?' becomes 'dust' (dust can mean a person's remains).
'gold'+'dust'='GOLD-DUST'
(Other definitions for gold dust that I've seen before include "Fine powder of precious metal" , "something much sought-after" , "Something valuable (and very rare?)" , "Proverbially rare stuff" .)