The story
From the Ancient Greek words for 30–90, which each ended in -κοντα (-konta). This ending might be ultimately related to Proto-Indo-European *déḱm̥ (“ten”), see e.g. τριάκοντα (triákonta).
Etymology from Wiktionary, CC BY-SA 4.0.
-conta-
Today it means: Combines with the prefixes for 3-9 to form complex prefixes referring to 30–90. Full definition →