A mug one may be sent out for (5)
I believe the answer is:
stein
'a mug' is the definition.
(stein is a kind of mug)
'one may be sent out for' is the wordplay.
'one may be' is an anagram indicator.
'out' means one lot of letters goes inside another.
'for' becomes 'i' (I can't explain this - if you can you should give a lot more credence to this answer).
'sent' is an anagram of 'sten'.
'sten' going around 'i' is 'STEIN'.
Can you help me to learn more?
(Other definitions for stein that I've seen before include "Gertrude __, avant-garde US author, d. 1946" , "Inset (anag.)" , "Glass" , "German earthenware beer mug" , "Large earthenware beer mug" .)