If you need to put the word by the icon (or in the icon), the icon has failed. At that point, you are admitting the icon is nonsensical and you might as well omit it.
EDIT:

How about this? Do you think this is clear? I used a handgun instead of a knife, because while a knife can be used for many things, handguns were designed to kill people. I used the yellow background because the icons are advisories, or warnings.
I think the circle symbols communicate the "sex" aspect, but I'm not sure about nudity. A fig leaf would look too much like "drugs"...
EDIT:

How about this? Do you think this is clear? I used a handgun instead of a knife, because while a knife can be used for many things, handguns were designed to kill people. I used the yellow background because the icons are advisories, or warnings.
I think the circle symbols communicate the "sex" aspect, but I'm not sure about nudity. A fig leaf would look too much like "drugs"...