"Identical" means like something else in every way.
to substitute
Yes, it does. An equation is something that equates something to something else, by means of the 'equals' sign.
The word 'additional' is not a noun; additional is an adjective, a word that describes a noun (a countable or uncountable noun).The noun form is addition; a countable noun as a word for something that you add to something else (an addition to a product line, an addition to a building); an uncountablenoun as a word for the act of adding something to something else (addition is the first step in learning math).
Intermittent
Something is imbedded in something else when it is stuck into it.
metaphor
Symbol, metaphor, simile.
It means to replace something, with something else that is equivalent.
It is same
In the chemical sense, it means something that dissolves something else. In the financial sense, it means basically "has money."
The word you may be looking for is "trade" or "barter," perhaps even "exchange."
dependancy
It means to mention and talk about something. It also means to have been recommended by someone else.
The word encompass means to encircle or to surround something. When something totally surrounds something else it is encompassed by it.
basically the same as something else depending on what your talking about
Impossible to answer - the word 'common' means you need to be comparing it to something else !