Barely make do, with "by" (3)
I believe the answer is:
eke
'barely make do with by' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for eke that I've seen before include "Make a laborious living" , "Increase, lengthen" , "Make a living laboriously - a palindrome" , "long ago" , "Supplement" .)