Soldier is not eccentric (7)
I believe the answer is:
regular
This might be a double definition.
'soldier' is the first definition.
(member of the regular army)
'not eccentric' is the second definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'is' acts as a link.
Can you help me to learn more?
(Other definitions for regular that I've seen before include "Normal or symmetrical" , "At set intervals" , "Frequent - usual" , "Even - constant" , "Perishes" .)