Give agent a chair for military update (6)
I believe the answer is:
sitrep
'a chair for military update' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.
'give agent' is the wordplay.
'give' becomes 'sit' (I can't justify this - if you can you should give a lot more credence to this answer).
'agent' becomes 'rep' (short for representative).
'sit'+'rep'='SITREP'
Can you help me to learn more?
(Other definitions for sitrep that I've seen before include "Report on current position (colloq.)" , "in which officers take an interest?" , "Italian family prominent in fifteenth and sixteenth century (Lucrezia -)" , "account by military" .)