If a Roman wanted to call another Roman a "bastard", what word would they use? I am curious about both the literal and general usage of the word, so calling someone an illegitimate child and also just someone who is a jerk. Bastardus itself is medieval latin, and I assume a latinization of the middle english word. Nothus might work for the former meaning, but did it ever expand to its usage to the latter?
For the literal meaning, there seem to have been two words, nothus and spurius. Whether there was a distinction in meaning isn't quite clear to me. L&S in the links above say the first meant an illegitimate child born of a known father, the latter one born of an unknown father; but they also say the latter is postclassical only (implying that in classical Latin the former meant both?). And the second-century grammarian Festus says that nothus is the Greek word for someone born out of wedlock, while we Romans refer to such a person as spurio patre natus.
Nothus is a Greek borrowing, and spurius has been thought to be a borrowing as well, maybe from Etruscan. It's a bit surprising that there seems to have been no native Latin word for the concept.
AFAIK (and more importantly, as far as L&S seem to know) these words did not become general-purpose insults like the English bastard. In English too it has only become a common term of abuse in the last 100-150 years, that is, just when the actual fact of being born outside wedlock has become less socially significant.