Growth in fancy stationery (4)
I believe the answer is:
cyst
'growth' is the definition.
(type of growth)
'in fancy stationery' is the wordplay.
'in' indicates the answer is hidden within the clue.
'CYST' can be found hidden inside 'fancy stationery'.
(Other definitions for cyst that I've seen before include "Abnormal body sac containing fluid" , "Closed sac in the body, containing fluid" , "Abnormal closed sac in a body" , "Sac, growth" , "pouch" .)