What's the difference between trilith and trilithon?

Trilith

Definition:

Example Sentences:

Definition:

(n.) A monument consisting of three stones; especially, such a monument forming a kind of doorway, as among the ancient Celts.

Example Sentences:

(1) Later, he was still more specific about the nature of this experience: it was English Heritage's job, he told me, to provide "entertainment" for the million-plus visitors who descend on the site every year, visitors who – as he put it – mostly "want a selfie with the trilithon".
(2) The stones were repeatedly moved and rearranged, and the enormous sarsen trilithons added, before the final outer circle of sarsen uprights and lintels was created around 1,900 BC, creating the world famous profile of the monument.
(3) If the aim of most neophyte visitors to the site is, as Thurley suggests, getting a selfie with a trilithon, then lingering in most of their minds is also an image of men with long white beards and long white robes doing stuff with sickles and mistletoe while raising their arms up to the rising sun.
(4) Of course, the Henge itself has been substantially remodelled over the centuries, never more so than during the last, when several stones were re-erected and lintels were replaced to form trilithons that hadn't been intact for a long time.