Understood it's in oak now; not pine (5)
I believe the answer is:
known
'understood' is the definition.
(similar in meaning)
'in oak now not pine' is the wordplay.
'in' indicates the answer is hidden within the clue.
'KNOWN' can be found hidden inside 'oak now not pine'.
'it's' is the link.
(Other definitions for known that I've seen before include "Famous" , "Apprehended mentally" , "Widely recognized" , "Acknowledged" , "In the public domain?" .)