Sloth for one is extremely sedate and idly disposed (6,3)
I believe the answer is:
deadly sin
'sloth for one' is the definition.
(sloth is a kind of deadly sin)
'extremely sedate and idly disposed' is the wordplay.
'extremely' means to remove the middle letters.
'disposed' is an anagram indicator.
'sedate' with its middle removed is 'se'.
'se'+'and'+'idly'='seandidly'
'seandidly' with letters rearranged gives 'DEADLY SIN'.
'is' is the link.
(Other definitions for deadly sin that I've seen before include "It's one of seven, gluttony say" , "not good - bad" , "Anger, say" , "Anger, covetousness, envy, gluttony, lust, pride or sloth" , "Eg, lust or gluttony" .)