こんにちは (Konnichiwa) toru e and イ リ ニ,
Thanks for the question!
toru e is 100% correct! 飲み (nomi) is the stem form of the verb 飲む (nomu) "drink." By itself it doesn't have any meaning, but the stem form is really handy for forming other grammar structures!
You can check out how to use the stem form in more detail in this brand new lesson on verbs:
One of the ways we can use this stem form is by adding it to すぎる (sugiru) "to exceed" to say something is "too much." Eg: 飲みすぎる (nomisugiru) "to drink too much."
You can read all about how to use すぎる (sugiru) in this lesson:
The すぎ (sugi) in のむすぎ (nomisugi) is the stem form of すぎる (sugiru). When you use a verb with the stem form すぎ (sugi), you can change the verb into a noun! That's why 飲みすぎる (nomisugiru) "drink too much" becomes 飲みすぎ (nomisugi) "over-drinking."
There are lots of of the nouns that use this same structure. For example:
- 食べすぎ (tabesugi) "over-eating"
- 寝過ぎ (nesugi) "over-sleeping"
- やりすぎ (yarisugi) "over-doing"
- 使いすぎ (tsukaisugi) "over-use"
Note that using すぎ (sugi) in the stem form like this is very casual, so you should only use it with friends and family.
I hope this helped! Please let me know if you have any other questions!
べんきょう を がんばって ください！ (Benykō o ganbatte kudasai!)