is there no way to differentiate between hot and warm? Is it just the same word?
I don't believe it's in use in modern Hindi, but I think the Sanskrit word was perhaps तपति? This is just a shot in the dark though, as I don't know Sanskrit. (https://en.wiktionary.org/wiki/%E0%A4%A4%E0%A4%AA%E0%A4%A4%E0%A4%BF#Sanskrit).
I can say, however, that the root of the word is tep*, from PIE, which is where we get 'tepid' in English :)
EDIT: I asked my Indian gf and she said it's गुनगुना, which means lukewarm/warm, but can't be used for things like weather (only water/food, etc.).
How hot is hot? How warm is warm? If you want it "piping hot," say garam-garam. If you want it "lukewarm", say kosā. If you want it in between, i.e. "warm-hot," say garam.
Garam is used for hot. For warm, we say 'halka/thoda garam' which basically translates to 'less hot'.
I'm sure there must be formal word that directly translates to warm but i told you the most common way native speakers say it.
When I was in New Delhi and asked at a shop to buy a bottle of water. The guy reached to give me refrigerated water. I said no. Then he handed me a different bottle and said Garam, and I understood it to mean room temperature. For the rest of my trip I asked for garam pani, and got what I wanted. So, is this another meaning of garam? It certainly was not hot water.
I'm guessing the reason it won't let me get away without the definite article is because "milk is hot" would be दूध गरम होता है or something?