Autism, as a word, is Latin for self-ism. It was named in the early days of Psychiatry by doctors who didn't understand what it was like for us. But what they noticed was, we seemed more preoccupied with ourselves than other people, so they called the condition self-ism in Latin.
Narcissism comes from the Greek myth of Narcissus, who was cursed by Nemesis to fall in love with his reflection (see Conon, Ovid). So Narcissism is also named after this idea of being preoccupied with yourself. And there hasn't been as much social progress on NPD, so a lot of people still think the same way today.
Etymologically speaking, the disorders are named pretty much the same. Early psychiatrists thought that these two conditions looked pretty similar to one another from the outside. And as someone with both autism and NPD, I get it, mate.
I've got reduced cognitive empathy from My autism, and the ability to voluntarily suppress affective empathy from My NPD. Affective empathy is the ability to sense others' feelings, and cognitive empathy is the ability to sense others' thoughts. So neurotypicals literally have a (limited) ability to read minds that we autistics don't get.
And a lot of the research literature says people with NPD can't sense others' feelings, but that's not My experience. I can choose not to feel others' feelings, when I want. I think I picked up the ability from being abused and guilt tripped as a kid. Now that I'm grown up, I get to choose whether I'm susceptible to attempts to abuse Me with My empathy. For example, a few weeks ago My bio mum told Me that My dead sister was abused by our adoptive parents, while I was the "golden child". My sister went out to suicide, so I think most egotypicals would get survivor's guilt from that. But I have NPD to protect Me from that kind of abuse, I'm used to shrugging that stuff off.
So there are lots of differences between the two. But also similarities. NPD is a mix of genetics and trauma, while autism is purely genetic. Both give Me meltdowns sometimes, when sensory stress or ego stress get to be too much. I have times when I have to mask both of them, and times when I don't and I might be accepted, or I might get in social trouble.
And both of them give Me a really acute sense of just how fake all of society is. Both of them motivate Me to defy social norms. Both give Me a strong justice sensitivity. I can't stand to see something I think is wrong or unfair.
So anyway, ask Me anything about living with NPD! I want to chat and make My experience of neurodivergence understood!