Design tailless aircraft (4)
I believe the answer is:
plan
'design' is the definition.
(synonyms)
'tailless aircraft' is the wordplay.
'tailless' means to remove the last letter (the tail of the word is removed).
'aircraft' becomes 'plane' (plane is a kind of aircraft).
'plane' with its last letter removed is 'PLAN'.
(Other definitions for plan that I've seen before include "Devise a way to achieve" , "Method laid out for accomplishing something" , "Agenda" , "Scheme - map" , "Off the right direction" .)