Supported, as in a plot (5)
I believe the answer is:
based
'supported' is the definition.
(similar in meaning)
'as in a plot' is the wordplay.
'in' is an insertion indicator.
'a plot' becomes 'bed' (bed is a kind of plot).
'as' going inside 'bed' is 'BASED'.
(Other definitions for based that I've seen before include "Founded, grounded" , "foundation" , "Worthless" , "Positioned" , "(Of aircraft) stationed" .)