Learner's definition of AMBITION
1 [count] : a particular goal or aim : something that a person hopes to do or achieve
My first ambition as a child was to be in the circus.
The wife of a famous poet, she had literary ambitions of her own. [=she wanted to be a writer too]
He has ambitions for an acting career. = He has ambitions to become an actor. = His ambition is to be/become an actor.
She finally achieved/realized/fulfilled her life's ambition [=the thing she most wanted to do in her life] when she started her own business.
2 [noncount] : a desire to be successful, powerful, or famous
He lacked ambition and couldn't compete with the others.
With her talent and fierce ambition [=her very strong desire to succeed], she became a very successful actress.
3 [noncount], US : a desire to do things and be active — usually used in negative constructions