What

is

an enemy?

What are some of the types of relationships you’ve encountered on your closest friends?

Frenemy does sound informal and colloquial, though, so I also suggest “rival” or “former rival”.

On a wild guess, might the circular motion required to operate a screw, render the expression “screwed” a sort of euphemism for more vulgar expressions like “fucked up” and so on.

Why any nails on the other hand can hold pieces of wood or walls together easily and give them more traction even before they turn into objects (like shoes/bags…).