First bit of pastrami inside dry bread, perhaps (6)
I believe the answer is:
staple
'bread perhaps' is the definition.
(bread is a staple food)
'first bit of pastrami inside dry' is the wordplay.
'first bit of pastrami' becomes 'p' (1st letter of 'pastrami').
'inside' means one lot of letters goes inside another.
'dry' becomes 'stale' (similar in meaning).
'p' put into 'stale' is 'STAPLE'.
(Other definitions for staple that I've seen before include "Fastening wire" , "One securing hasp; principal" , "security device" , "Short U-shaped paper fastener" , "wool" .)