Periodically laugh at Turkish commander (3)
I believe the answer is:
aga
'turkish commander' is the definition.
(term for an Ottoman military commander)
'periodically laugh at' is the wordplay.
'periodically' means one should take alternating letters (letters must be selected 'every so often').
'laugh'+'at'='laughat'
The alternating letters of 'laughat' are 'AGA'.
(Other definitions for aga that I've seen before include "Oven" , "Turkish governor" , "Eastern potentate" , "Chief officer" , "- Khan, Ismaili leader" .)