NB: fresh issue has just been delivered! (7)
I believe the answer is:
newborn
'nb fresh issue has just been delivered' is the definition.
I can't tell whether this defines the answer.
'fresh issue has just been delivered' is the wordplay.
I cannot really see how this works, but
'fresh' could be 'new' (synonyms) and 'new' is found within the answer.
'delivered' could be 'born' (as in a baby being delivered) and 'born' is found within the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for newborn that I've seen before include "Recently delivered" , "Just entered the world" , "Young baby" , "Neonate" , "Recently given birth to" .)