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' indicates alternate 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" .)