Be without one scheme for flier (7)
I believe the answer is:
biplane
'flier' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'be without one scheme' is the wordplay.
'without' is an insertion indicator ('without' can be similar in meaning to 'outside').
'one' becomes 'I' (Roman numeral).
'scheme' becomes 'plan' (synonyms).
'i'+'plan'='iplan'
'be' enclosing 'iplan' is 'BIPLANE'.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for biplane that I've seen before include "Old aircraft" , "craft" , "flying machine" , "Early aircraft" , "Eg, Tiger Moth" .)