Recalled Administrative Officer enclosing precious item in last letter (5)
I believe the answer is:
omega
'last letter' is the definition.
(last letter of the Greek alphabet)
'recalled administrative officer enclosing precious item' is the wordplay.
'recalled' shows that the letters should be reversed in order (to recall can mean to bring something back).
'administrative officer' becomes 'ao' (this might be a standard abbreviation I've not previously seen).
'enclosing' is an insertion indicator.
'precious item' becomes 'gem' (I've seen this in another clue).
'ao' going around 'gem' is 'agemo'.
'agemo' in reverse letter order is 'OMEGA'.
'in' is the link.
Can you help me to learn more?
(Other definitions for omega that I've seen before include "letter from abroad" , "Conclusion" , "Last thing" , "long letter" , "Final outcome" .)