ano
ES [ˈano] · one tilde away from año (“year”) · spelled exactly like Czech ano (“yes”)
I once wrote a birthday message on a borrowed laptop with no ñ key and congratulated somebody on their anos. Up to that point I had quietly filed the tilde under decoration.
Czech makes it worse rather than better. Ano is Czech for yes, so the word arrives at me looking like agreement and nothing else, which is precisely the wrong instinct to bring into Spanish. These days I give that tilde the respect you would give exposed wiring.
Three words and not a single link between them. Spanish año is Latin annus, the year, and the squiggle over the n is the worn-down remains of the double n it used to carry. Spanish ano is a different Latin word altogether, anus, which meant a ring - the same ring that gives English annular. Czech ano is older and plainer than either, inherited from Proto-Slavic with nothing Latin anywhere near it. So the tilde is carrying more weight here than any other mark in Spanish. Leave it off and a polite question about somebody's age turns into something nobody wanted to ask.