By luck, perchance? (3)
I believe the answer is:
per
'by' is the definition.
(I've seen this in another clue)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for per that I've seen before include "Preposition indicating by means of" , "According to" , "For each or every" , "Preposition meaning for each" .)