I wonder if it is possible for a word to mean its opposite. It would kind of defeat the purpose if you ask me. But the reason I think that such a word exists is that languages were not really designed, they just kinda morphed into being. English is full of ambiguities but never just in a single word. An example from the always good Matthew Good.
I will make you a weapon.
Does this mean “I will make a weapon for you” or “I will turn you into a weapon”?
I’m sure in all the languages of the worlds at least one of them has a word like that. And I don’t mean like “aloha” or “shalom” which are both a welcoming greeting and a departure salutation. The people who came up with those words were confused. I’m more thinking of a word like “install” or “activation” something along those lines. I bet you German has one because in German one can simply take words and glue them together to make a bigger word. For example
The black belt ceremony was boring.
would become
Die Schwarzegürtelzeremonie war langweilig.
It’s really a great language, one can have lots of fun with it. Anyway, if anyone out there has such a word and you feel like sharing, I would love to hear it.
like the ashtray / garbage can combinations they have over here - and yes, the garbage is on fire
Die Hard Three 
Laeding word-creator: German legislature:
Arbeitnehmeraufwendungsausgleichsgesetz (AAG)
Asylzuständigkeitsbestimmungsverordnung (AsylZBV)
Betriebsverfassungsreformgesetz (BetrVRG)
–> Many people dealing with law suffer from “Aküfi” (Abkürzungsfimmel)…
I guess the Germans (and Austrians) are just used to reading words that are all stuck together. As a native English speaker I find it really hard. And I have been unable to find a translation for “Abkürzungsfimmel”…
Fast: 1) Rapid movement “The boat sailed fast.”
2) No movement “The boat was held fast to the dock.”
3) No quenching of appetite “I’m fasting”
4) Complete submission to appetite “She’s fast”.
😉
I’m think more of a single word that in an identical sentence can have two meanings and those meaning are opposite. Kinda like “Aloha, my friend” but not using aloha.