No, act is not a synonym for tax. Add may be a better word.
possession
One synonym for the phrase "trade route" could be commercial pathway.
Native American is the most common synonym for North American Indian/
acceptable
the answer for inside is interior
I slithered down the muddy bank of Indus river.
The verb form slithered does not have an adverb form. There are adjectives slithery and slithering.
glide
There are 11 syllables in "beside your shoe it slithered round."
Slithered
You could use inside.
The slit grew wider as the material stretched. He cut a slit into the side of the animal.
Empty or has nothing inside
confidential, inner, indooor
In the sentence the slimy, green snake slithered through the tall grass the nouns are snake and grass
He slithered helplessly down the slope.