Level, even (4)
I believe the answer is:
flat
This clue is a double definition.
'level' is the first definition.
(synonyms)
'even' is the second definition.
(similar in meaning)
(Other definitions for flat that I've seen before include "Level - uninteresting - accommodation" , "In music, below the correct pitch" , "Small residence - lacking sparkle" , "Absolutely" , "No longer charged" .)