Condescend to accept second plan (6)
I believe the answer is:
design
'plan' is the definition.
(synonyms)
'condescend to accept second' is the wordplay.
'condescend' becomes 'deign' (synonyms).
'to accept' indicates putting letters inside.
'second' becomes 's' (common abbreviation).
'deign' enclosing 's' is 'DESIGN'.
(Other definitions for design that I've seen before include "Prepare a plan for something to be made" , "Devise, dreate, make out a plan" , "End" , "Provide blueprint" , "Drawing before an object is made" .)