Just reason for building a showplace (10)
I believe the answer is:
fairground
'a showplace' is the definition.
The definition and answer can be both locations as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'just reason' is the wordplay.
'just' becomes 'fair' (just can mean fair in the sense of showing justice).
'reason' becomes 'ground' (synonyms).
'fair'+'ground'='FAIRGROUND'
'for building' acts as a link.
Can you help me to learn more?
(Other definitions for fairground that I've seen before include "that holds attractions" , "rides here" , "Scary ride here perhaps" , "Entertainment venue" , "good enough for entertainment" .)