Learn English – Difference between the words “betrayal” and “treachery”

As defined from the NOAD, grammar is, "the whole system and structure of a language or of languages in general, usually taken as consisting of syntax and morphology (including inflections) and sometimes also phonology and semantics."

It includes the syntax, but it's not limited to that.

The syntax of a language is, "the arrangement of words and phrases to create well-formed sentences in a language."
For example, the syntax is about which order subject, verb, and object have in a sentence to form a well-formed sentence. A sentence like "like it I" is not considered a well-formed sentence, basing on the English syntax, even if people would understand that the correct sentence is "I like it."

Consider this crude picture I whipped up:

The material making the red part is probably some form of rigid metal wire, or maybe a modern composite. The material in the blue part could be wood, metal, plastic, or again a composite. The material in the black part can be called either net or netting.

The entire device is called a net. Specifically, this drawing depicts a butterfly net. If anyone called it a butterfly netting, I would think it very strange.

In your own sources, notice that "netting" has only one definition, beginning with "material" whereas "net" has multiple definitions- this first refers to material again, but the second talks about the "piece" put to a specific purpose. Here is another dictionary giving very similar results.

Similarly, wikipedia has seperate pages for net (device) and net (textile) where only the latter mentions it can also be called netting.

_{Note: I have assumed you only care about the use of the two words as nouns. As verbs, then of course "netting" is the participle of "to net."}