Most lenient with my muddles (9)
I believe the answer is:
eminently
'most' is the definition.
(thesaurus)
'lenient with my muddles' is the wordplay.
'with' says to put letters next to each other.
'muddles' indicates an anagram (I've seen 'muddle' mean this).
'lenient' put after 'my' is 'mylenient'.
'mylenient' with letters rearranged gives 'EMINENTLY'.
(Other definitions for eminently that I've seen before include "to a notable extent" , "In an outstanding manner" , "well" .)