(idiomatic) To be (or to place oneself) in a risky, potentially dangerous or delicate situation.

(idiomatic) Something that if allowed or accepted to a small degree would lead to systematic encroachment.

Alternative form of thin end of the wedge

(idiomatic) From nowhere or nothing; from a non-existent or unknown source.

present participle of skate on thin ice

plural of thin-film interference

(uncountable, optics) Interference of light caused by its reflection from both boundaries of a thin film of a transparent material. / (countable, optics) An instance of this interference.

A form of transistor manufactured by depositing layers of semiconductor, dielectric and metal on a substrate

(nautical) A fiddle block.

(colloquial) The police.