IPA: /ˌoʊ.vɚ.æmˈbɪʃ.əs/
KK: /oʊvəræmˈbɪʃəs/
Having goals or desires that are too high or unrealistic, often leading to disappointment or failure.
His overambitious plans for the project worried his team.
Overambitious → It is formed from "over-" (meaning excessively) and "ambitious" (from Latin "ambitiosus", meaning eager for advancement). The word "overambitious" describes someone who is excessively eager for success or advancement beyond reasonable limits.
Think of someone who is 'excessively' ('over-') eager for success — that's what overambitious means.