Meaning of “thin” - Learner’s Dictionary

thin

adjective uk us /θɪn/ (thinner, thinnest)
DISTANCE

A2 Something that is thin is smaller than usual between its opposite sides:

a thin slice of ham
The walls are very thin.
PERSON

A2 A thin person or animal has very little fat on their body.

LIQUID

A thin substance or liquid has a lot of water in it and flows easily:

thin soup
AMOUNT

having only a small number of people or a small amount of something:

Government troops were very thin along the border.
His hair is going thin on top.
AIR

Thin air does not have enough oxygen in it.

→ See also disappear/vanish into thin air , be thin on the ground , through thick and thin , wear thin

(Definition of “thin adjective” from the Cambridge Learner’s Dictionary © Cambridge University Press)