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

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