Going around unknown, vacant citadel besieged by army chief (6)
I believe the answer is:
cyclic
'army chief' is the definition.
Both the definition and answer are adjectives. Perhaps they are linked in a way I don't understand?
'going around unknown vacant citadel besieged' is the wordplay.
'going around' indicates putting letters inside.
'unknown' becomes 'y' (algebra).
'vacant' says to hollow out the word (remove centre letters) (a vacant or emptied out form of the word).
'besieged' becomes 'cic' (I can't justify this - if you can you should believe this answer much more).
'citadel' with its middle removed is 'cl'.
'y'+'cl'='ycl'
'ycl' inserted inside 'cic' is 'CYCLIC'.
'by' acts as a link.
Can you help me to learn more?
(Other definitions for cyclic that I've seen before include "So-so hotshots are" , "Having the form of a closed ring" , "Recurrent" , "Arranged in a ring structure" , "Occurring in a repeating sequence" .)