Admitting old part of house accommodates new (6)
I believe the answer is:
owning
'admitting' is the definition.
(I've seen this before)
'old part of house accommodates new' is the wordplay.
'old' becomes 'o' (abbreviation).
'part of house' becomes 'wing'.
'accommodates' is an insertion indicator.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'wing' going around 'n' is 'wning'.
'o'+'wning'='OWNING'
(Other definitions for owning that I've seen before include "Possessing" , "Being in possession or confessing" , "In legal possession of" , "Possesing" , "Conceding - possession" .)