"I'm dry" meaning "Would you buy me a drink?" What semantic or rhetorical term describes such usage?

Solution 1:

It's an example of...

circumlocution - also called circumduction, circumvolution, periphrasis, or ambage
- an ambiguous or roundabout figure of speech

All those alternatives are "wordy" words. In common speech we're more likely to call it...

beating around/about the bush
- if you beat around the bush, or beat about the bush, you don't say something directly

So "I'm thirsty!" may just be a (slightly) roundabout way of saying "Give/Buy me a drink!". That kind of "oblique meaning" will be obvious to all native speakers, but some are idiomatic usages that simply have to be learned. So a man saying "I have to see a man about a dog" (or a woman saying "I have to powder my nose") often means exactly and only "I'm going to the toilet to urinate".

Solution 2:

I'd use the word hint for this type of speech.

When someone says "I am thirsty," hoping it will be understood as "Please give me a drink," I would say they are hinting that they would like a drink.

Merriam-Webster defines hint (as a verb) as "to convey indirectly and by allusion rather than explicitly," and offers as synonyms allude, imply, indicate, infer, insinuate, intimate and suggest.

(Infer doesn't seem appropriate to me, however. She implied that she would like a drink correctly describes the above situation, but She inferred that she would like a drink is definitely not correct. Note also that intimate should be understood to be used in its verb form, not as the more common adjective.)

Solution 3:

Unfortunately I could not find the graph either in english nor in german that I was looking for.

At school we learned, that there are different layers of semantics and we had a nice graph with a rectangle and arrows. Well, I can't find it, so forget about that. The thing I remember is that our teacher came into the classroom that day saying "Oh, it is a little cold in here.". Someone got up and closed the window. He smiled, telling us he just introduced todays topic.

"It is cold in here." does of course mean that he feels cold. But, in relation to the fact that the window is open, it also codes for his wish to have that closed. A lot of people in the room intuitively inferred that meaning. In german he called those different levels or layers of semantics. Unfortunately, semantic layers in english is not necessarily related to language and I don"t know what it would be scientifically called.

In the picture we had speaker, recipient, context and message, I think. Whithout context, the recipient can only decode the literal meaning of the message, but with context he can also receive the additional hidden sub-message.

This, of course does not answer your question by giving you the correct name, but maybe someone knows the name for this.