African leaves End of Watch by King, old volunteers taken aback (4)

'african' is the definition.
Both the definition and answer are singular nouns.
Maybe there's an association between them I don't understand?

'end of watch by king old volunteers taken aback' is the wordplay.
'end of' indicates one should take the final letters.
'by' means one lot of letters go next to another.
'king' becomes 'K' (chess abbreviation).
'old volunteers' becomes 'TA' (Territorial Army, former name of the Army Reserve).
'taken aback' says the letters should be written in reverse.
The last letter of 'watch' is 'h'.
'ta' in reverse letter order is 'at'.
'h' put after 'k' is 'kh'.
'kh'+'at'='KHAT'

'leaves' acts as a link.

Can you help me to learn more?