Existing as an essential constituent (7)
I believe the answer is:
inbuilt
(Other definitions for inbuilt that I've seen before include "essential" , "Fitted" , "Present from the beginning" , "Native" , "Integral" .)
I believe the answer is:
inbuilt
(Other definitions for inbuilt that I've seen before include "essential" , "Fitted" , "Present from the beginning" , "Native" , "Integral" .)