No difference. Same word-different spelling and pronounciation.

Ancient Greek papyri (Egyptian provenance) often show interchange between t and d.

Okay. As a native greek speaker, I can give my opinion on a couple of things:

• Each language has it's own unique grammar characteristics, and one obviously cannot compare each and every one of them with the ones of their native language. In this case, one can't compare each and every English grammar rule with every Greek one.

• There might be a slight confusion in written Greek, in a few cases, but absolutely none in spoken, as long as the learner knows a proper and basic sentence structure.

In your examples, there could be confusion only in written Greek, because in spoken Greek, the context depends on numerous things, such as

• possibly another sentence following

• The subject of your conversation

• Common sense

and possibly more. I think you'll get the idea in the examples I'll give below.

• Greek is a language strictly based on some vital rules. Yes, some sentence structures do get altered, and yes, some words are interchangeable in many cases, but they are commonly and daily used. Basic Greek rules do not get ignored, just altered to a logic extent.

So, let's see a couple of examples.

Let's say you're at a bar. Your friend points at a group of men sitting across the bar, saying "Το κρασί των αντρών είναι κόκκινο." Ιf you looked at where she's pointing at, and see a group of men all drinking red wine, you'd be sure that she's talking about that specifc group of men, not men's wine in general. (even if she doesn't use αυτών or εκείνων. If they were the only men in the room, it would be perfectly logical.)

Let's say you're at a perfume store. Your female friend wants to buy a perfume, you pick one for her and she says "Οχι, αυτό το άρωμα είναι για άντρες/ είναι αντρικό" (article τους ommited, since you're talking about men in general. This is a general rule, and I'm mentioning it since I'm not sure if you're aware of it or not ^.^). You couldn't possibly be confused about this one, even if you're friend doesn't say αντρικό.

So as you see, it purely depends on the occasion, due to some words being interchangeable (αντρικό/για άντρες, των αντρών/εκείνων-αυτών των αντρών).

Lastly, about the glass of water:

Θέλω ένα ποτήρι (με) νερό - I want a glass of water.

(I noticed you mentioned that it has other meanings, but it doesn't. Το ποτήρι νερό means the glass containing water, nothing else.)

Θέλω ένα ποτήρι του νερού/νεροπότηρο - I want a water glass.

Το ποτήρι του νερό is wrong.

I hope this is a bit helpful. ^.^

In general, plural genitives have accent no further than the penult, because the omega in the final syllable used to be a long vowel and the accent couldn't fall on the antepenult in Ancient Greek if the final syllable was long.

The exact rules are tricky and depend partly on the form that the word had in Ancient Greek.

Easiest are probably words in -ος -ο -ι: the first two are accented on the ultima if the basic form is or on the penult otherwise; the last one is always on the ultima.

Neuter nouns in -μα are also easy: gen.pl. is -μάτων.

Words in -α -η -ας -ης depend on the form they had in Ancient Greek, in general.

men's is correct. The ' (apostrophe) is used to show something that belongs to the "men".

άντρας, άνδρας are both correct for "man"

-τδ- is not possible.