Straying (6)
'straying' is the definition.
('err' can be a synonym of 'stray')
This is the entire clue.
(Other definitions for erring that I've seen before include "Being incorrect" , "Going wrong" , "Making 7 down" , "taking wrong direction" , "Sinful" .)
'straying' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for errant that I've seen before include "Travelling in search of adventure like knight of old" , "Like many a knight" , "Misbehaving" , "Quixotic" , "Straying from the right course" .)