-ίτης

• -ῖτις (-îtis) – feminine

Back-formation from πολῑ́της (polī́tēs), from πόλις (pólis, “city”) +‎ -της (-tēs). The ῑ from the stem of πόλις became part of the suffix: πολῑ́-της was reanalyzed as πολ-ῑ́της (pol-ī́tēs).

-ῑ́της • (-ī́tēs) m (genitive -ῑ́του); first declension

1. Suffix forming a masculine noun: one connected to, a member of; one from a particular place (demonym)

Originally forming generic adjectives, such as πολ-ίτης (pol-ítēs, “one from the city, citizen”) from πόλις (pólis, “city”); ὁπλ-ίτης (hopl-ítēs, “one with armour, hoplite”) from ὅπλον (hóplon, “large shield”).

But by the Hellenistic period, both the masculine -ίτης (-ítēs) and the feminine -ῖτις (-îtis) became very productive in forming technical terms for products, diseases, minerals and gems (adjectives with elliptic λίθος (líthos, “stone”)), ethnic designations and Biblical tribal names. These technical uses survive in modern languages in Greek loanwords for diseases (in -itis), for minerals (in -ite) and for nations, tribes or religious sects (plurals in -ites), partly also in common nouns such as hermit.

• Latin: -ītēs

• Smyth, Herbert Weir (1920), “Part III: Formation of Words”, in A Greek grammar for colleges, Cambridge: American Book Company, § 843