Belonging to, or proceeding from, the original stock; native; hence, not counterfeit, spurious, false, or adulterated; authentic; real; natural; true; pure; as, a genuine text; a genuine production; genuine materials.
If you are referring to synthetic meaning "man-made", then the opposite would be "natural" or "genuine". There is another usage of synthetic, in which the opposite is "analytic".
Real, genuine.
real, genuine
The opposite could be true, or real, genuine.
genuine, real
The opposite of bastard is genuine and/or born within wedlock, of identifiable roots.
what is opposite meaning of lucid
Haram (Muslim word for "not clean/genuine")
Genuine, natural, real, unaffected, unpretentious
it means poops out
it means real or pure
mindedness...........