When something becomes dense or heavy, the word "thick" might be used to describe it. This is a word that is also used to describe how wide something is. The opposite of thick is thin.
The ice on the lake is six inches thick.
These wooden boards are two inches thick.
A thick layer of mud covered the streets after the storm.
Hot tropical air feels wet and thick.
A thick fog rolled in off of the lake and made driving difficult.
When you add flour to batter it becomes thick.
This is a thick piece of chocolate cake.
The word "thickness" is a noun:
Steel beams in a skyscraper must be of a certain thickness in order to hold the building up.
The thickness of the forest made it difficult to walk through.
The trees, bushes and plants create a thick forest.
To thicken something is to make it thicker. This word is a verb.
simple
past
past participle
thicken
thickened
thickened
A sauce can be thickened with flour or corn starch.
The surface of a lake thickens quickly into ice once the temperatures go below zero degrees Fahrenheit.
The trees, bushes and plants create a thick forest.