In Dunmeri mythology we attribute the creation of the Morag Tong with the Daedric Prince Mephala who spins the webs that all secret plots of murder are attached to but the mystery of the Morag Tong is their name. In Dunmeri Morag Tong means "The Forester Guild" why are they called this?

My theory is a simple one, some scholars believe that originally the teachings of Mephala were actually that of Hermaeus Mora this can be furthered by the Morag Tong's name, I believe the Morag Tong were once the Foresters of the forbidden or knowledge forest (We have yet to determine what Hermaeus means but Forbidden or Knowledge both sound suitable for him)

I believe the Morag Tong were once a order of scholars who sought out all things forbidden and guessing by that they had to remain in the shadows which might also explain how Mephala managed to become one of the Good Daedra. Somehow the Morag Tong lost their way of knowledge and instead found the way of espionage and assassination.

I am probably way off but I thought I remember something about HM being referred to as the old man of the forest in dragonborn dlc? Maybe connection there.

In nordic mythology Herma-Mora was known as the demon of Knowledge and was called the Woodland Man.

In other words, shrug.

Meh, I like my idea better

After the Nords were driven out, and the Dwemer had disappeared, the Tong regressed to killing their own. Thug life.

It is known that Mephala and Hermaeous Mora are "siblings" in such a way that it's mortally perceived; that is to say, it's written about somewhere, so I could see where you draw such conclusions. They both hold sway over mortality, Hermaeous with Intellect, Mephala with emotion. But the Tong is the Foresters Guild in the sense of the book titled 'the Axe Man', or somesuch. They are a pureform order of mendicant murderers, not an Order to Intellect.

Concisely, the tong are using an aspect of MEPHAL in their name. An inverse of tact, a poetic truth. They are those with axes, to cleave, rend and hew the forests. Forests being mortals. This enacts either guileful murder or genocide.