Class throw eggs at first (5)
I believe the answer is:
caste
'class' is the definition.
(type of social class)
'throw eggs at first' is the wordplay.
'throw' becomes 'cast' (synonyms).
'at first' says to take the initial letters.
The initial letter of 'eggs' is 'e'.
'cast'+'e'='CASTE'
(Other definitions for caste that I've seen before include "Social status" , "Hereditary class (in India)" , "Brahmans for instance" , "Division of Hindu society" , "Hereditary social class among Hindus" .)