In English grammar, an intensifier is a word that modifies - increases or decreases - the meaning or effect of another word. Intensifiers are used to boost, emphasise or add force to the meaning of another word. The other word can be a noun, verb, adjective or adverb.
Intensifiers can often be both positive and negative. For example: That boy is remarkably intelligent/That boy is remarkably stupid. Also, some intensifiers can have the same meaning. For example, rapidly and quickly.
The list of intensifiers is very long. However, some commonly-used intensifiers are too, much, so, slowly, enough, really, terribly, strongly, little, fairly and extremely.
Here are examples of intensifiers in use: