While at this, had nothing specific to do and slackened, reportedly (5,3)
I believe the answer is:
loose end
'while at' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'had nothing specific to do and slackened reportedly' is the wordplay.
I cannot really understand how this works, but
'had' could be 'd' (in contractions e.g. 'I'd', 'you'd' etc) and 'd' is found in the answer.
'nothing' could be 'o' (looks like zero - 0) and 'o' is located in the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is found in the answer.
'reportedly' could be 'e' (I've seen this in other clues) and 'e' is present in the answer.
The remaining letters 'lose' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'this' acts as a link.
Can you help me to learn more?
(Other definitions for loose end that I've seen before include "One's not yet decided" , "Detail not yet settled" , "Unsettled matter" , "should have been tied?" , "The bored, idle at one" .)