A thousand for key money? (5)
I believe the answer is:
grand
'a thousand' is the definition.
(synonyms)
'key money?' is the wordplay.
'key' becomes 'g' (I've seen this in other clues).
'money?' becomes 'rand' (I've seen this before).
'g'+'rand'='GRAND'
'for' is the link.
(Other definitions for grand that I've seen before include "One thousand pounds" , "Impressive, large" , "A slangy PS1,000" , "Designed to impress" , "GBP1,000" .)