Desert herdsman happened to look sideways (8)
I believe the answer is:
cameleer
'desert herdsman' is the definition.
The definition suggests a singular noun which matches the answer.
'happened to look sideways' is the wordplay.
'happened' becomes 'came' (to happen upon and to come upon mean to encounter).
'to' is a charade indicator (letters next to each other).
'look sideways' becomes 'leer' (leer is a kind of look. I am not sure about the 'sideways' bit.).
'came'+'leer'='CAMELEER'
Can you help me to learn more?
(Other definitions for cameleer that I've seen before include "Desert traveller" , "one in a caravan maybe" , "One driving across the Sahara" , "Driver" , "One journeying across the sands" .)