Mitigators are the opposite of intensifiers. When we want to make an adjective less strong we use these words:
减弱是增强的反义词。当我们想弱化使用的形容词：

fairly - rather - quite

By the end of the day we were rather tired.

The film wasn’t great but it was quite exciting.

and in informal English: pretty

We had a pretty good time at the party.

We call these words mitigators.

Mitigators with comparatives:
比较级的减弱词：

We use these words and phrases as mitigators:

a bit - just a bit - a little - a little bit - just a little bit - rather - slightly

She’s a bit younger than I am.

It takes two hours on the train but it is a little bit longer by road

This one is rather bigger.

We use slightly and rather as mitigators with comparative adjectives in front of a noun:
我们用slightly和rather作为减弱词与比较级形容词连用，放在名词前面：

This is a slightly more expensive model than that.

This is rather bigger one than that.

Adjectives as intensifiers:

We use some adjectives as intensifiers:
我们用形容词作为减弱词：

absolute

total - complete

utter - perfect

real

We say:

He’s a complete idiot.

They were talking utter nonsense.

… but we do not say:

The idiot was complete.

The nonsense they were talking was utter.