-τρον

Etymology
From, from.

Synonyms
-θρον (πτολίεθρον, city), -τλον (χύτλον, libation), -θλον (ἄεθλον, contest), -θρη, -θλη (γενέθλη, race).

For roots ending in σ, the suffix always has τρ. Older forms in which the root does not contain a liquid or end in σ tend to use the τλ/θλ forms, but there are many exceptions, such as σκῆπτρον, scepter, and κέντρον, center.