IPA: /æmˈbɪʃənləs/
KK: /æmˈbɪʃənləs/
Lacking the desire to achieve or succeed; not having goals or aspirations.
He felt ambitionless after years of working in a job that didn't inspire him.
Ambitionless is formed from "ambitio" (from Latin, meaning a desire for success or honor) and "-less" (meaning without). The word describes a state of being without ambition or desire for success.
Think of 'ambition' as a strong desire for success, and '-less' means without. So, ambitionless means being without that strong desire.