Genius, good man inspired by old oath (7)
I believe the answer is:
egghead
'genius' is the definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'good man inspired by old oath' is the wordplay.
'good' becomes 'g' (abbreviation).
'man' becomes 'he'.
'inspired by' means one lot of letters goes inside another.
'old oath' becomes 'egad' (I've seen this before).
'g'+'he'='ghe'
'ghe' placed within 'egad' is 'EGGHEAD'.
Can you help me to learn more?
(Other definitions for egghead that I've seen before include "providing access to soldiers" , "Intellectual, studious academic" , "where soldiers may take a dip?" , "Very clever person" , "Brainy type" .)