Release the mildly erroneous three (4)
I believe the answer is:
free
'release' is the definition.
(synonyms)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for free that I've seen before include "Costing nothing" , "Exempt" , "Not occupied; release" , "Unfettered" , "Untrammelled" .)