Family with first of loaves in oven (4)
I believe the answer is:
kiln
'oven' is the definition.
(I know that kiln is a type of oven)
'family with first of loaves' is the wordplay.
'family' becomes 'kin' (synonyms).
'with' means one lot of letters goes inside another.
'first of loaves' becomes 'l' (kst letter of 'loaves').
'kin' placed around 'l' is 'KILN'.
'in' acts as a link.
(Other definitions for kiln that I've seen before include "Pottery-firing oven" , "Industrial furnace" , "Oven for firing pottery" , "Potter's Friend" , "Industrial oven" .)