Lighten up foes to possibility of minor error in speech (4,2,3,6)
I believe the answer is:
slip of the tongue
'minor error in speech' is the definition.
I can't judge whether this defines the answer.
'lighten up foes to possibility' is the wordplay.
'possibility' is an anagram indicator (another possible arrangement of the letters).
'lighten'+'up'+'foes'+'to'='lightenupfoesto'
'lightenupfoesto' anagrammed gives 'SLIP OF THE TONGUE'.
'of' is the link.
Can you help me to learn more?
(Other definitions for slip of the tongue that I've seen before include "vocal error" , "Error in words" , "mistake one hears" , "a small error" .)