Quirky law from east binding that chap thus (9)
I believe the answer is:
whimsical
'quirky' is the definition.
(I've seen this before)
'law from east binding that chap thus' is the wordplay.
'from east' says the letters should be written in reverse (letters written right to left or 'east to west').
'binding' indicates putting letters inside.
'that chap' becomes 'him' (I've seen this in another clue).
'thus' becomes 'sic' ('thus' in Latin).
'law' in reverse letter order is 'wal'.
'him'+'sic'='himsic'
'wal' going around 'himsic' is 'WHIMSICAL'.
(Other definitions for whimsical that I've seen before include "Mischievous" , "Playfully fanciful" , "Delicately playful" , "odd" , "Playfully quaint" .)