Plan that is a recurring idea, but not initially (6)
I believe the answer is:
scheme
'plan' is the definition.
(scheming is a kind of planning)
'that is a recurring idea but not initially' is the wordplay.
'that is' becomes 'sc' (abbrv. for Latin scilicet; 'namely').
'a recurring idea' becomes 'theme' (I've seen this in another clue).
'but not initially' means to remove the first letter.
'theme' with its first letter taken off is 'heme'.
'sc'+'heme'='SCHEME'
(Other definitions for scheme that I've seen before include "Systematic of crafty plan of action" , "Secret plan, plot" , "Design" , "Connive, intrigue" , "Conspire" .)