IPA: /ˌoʊvərˈzeləsnəs/
KK: /oʊvərˈzeləsnəs/
The quality of being very enthusiastic or eager, often to an excessive degree.
His overzealousness in promoting the project made some team members uncomfortable.
Overzealousness → It is formed from "over-" (meaning excessively) and "zealous" (from Greek "zelos", meaning fervor or enthusiasm) combined with the suffix "-ness" (meaning the state of being). The word describes the state of being excessively enthusiastic or fervent about something.
Think of being 'excessively' ('over-') enthusiastic ('zealous') — that's what overzealousness means.