Wander off - say about two fifths of a metre (5)
I believe the answer is:
stray
'wander off' is the definition.
(I've seen this in another clue)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for stray that I've seen before include "Depart from the right path" , "Go off course" , "Deviate" , "Wander; be unfaithful" , "out of place" .)