New piece of ground that's acquired for buttons (5)
I believe the answer is:
nacre
'that's acquired for buttons' is the definition.
(buttons may be made of nacre or mother-of-pearl)
'new piece of ground' is the wordplay.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'piece of ground' becomes 'acre' (a piece of land).
'n'+'acre'='NACRE'
(Other definitions for nacre that I've seen before include "Mother of pearl" , "Pearl's mum" , "Constituent of inlay furniture" , "Mother-of-pearl from shellfish" , "inside of shell" .)