Substitute could be an adjective or a noun.
For example,
"The substitute teacher" uses subtitute to describe what kind of teacher.
"The substitute passed out the homework" uses substitute as a noun by itself
It depends on how you use the word. "Substitute" can be a noun, verb or adjective. As a noun: Our substitute wasn't nearl as nice as our regular teacher. As a verb: When cooking, you can substitute honey for sugar if you reduce the amount of other liquids. As an adjective: The substitute goalie helped our team make it to the playoffs.
A word such as a number or article or possessive adjective that determines or limits the meaning of a noun phrase. For example their in their black cat. Other articles are 'the, a and an' or any words that might substitute for them - yours their, some and each
You substitute the variable for its value. Or you substitute the variables for each of the values.
Cautious IS an adjective. An adjective is an action!
The word "it" is not an adjective (it is a pronoun). A word is an adjective if it modifies (defines, characterizes) a noun or pronoun. The big tent - big is an adjective He is tall - tall is an adjective This key - this (while arguably called a determiner) is a demonstrative adjective
Severe is an adjective.
An adjective
The adjective is ambiguous.
The word is manifest (in the adjective sense).
The adjective is indivisible.
The adjective could be obsolete, outmoded, or superseded.
The adjective is probably "cushy."
The adjective would be invincible. (unbeatable)
The adjective could be moral, ethical, honorable, or righteous.
An adjective meaning free from error could be flawless or perfect.
The adjective for such speech is "heartfelt." The person may be "earnest" or "sincere."
The term might be skeptic. Another adjective for skeptical is suspicious.
As an adjective, ersatz means "made in imitation". As a noun, an ersatz is something which is made in imitation, as an effigy or substitute for the original.