The word “ambition” is indeed vague, and this is unfortunate, as there is a rich vocabulary full of distinction we ought to be using. (You see the same thing when people use “passionate” as a virtue, such as in job postings when what they mean is “enthusiastic”. Taken literally, you certainly don’t want passionate employees!)

In the strict sense, ambition [0] is an inordinate love of honor.

Perseverance [1], OTOH, is the ability to endure suffering in pursuit of a good. Both effeminacy (refusal or inability to endure suffering to attain a good) and pertinacity (obstinate pursuit of something one should not) are opposed to perseverance.

It seems that ambition is therefore opposed to perseverance, since it can either be effeminate (the ineffectual daydreamer that makes big plans that he never realizes) or pertinacious (the person who bites off more than he can chew).

Prudence [3] involves the application of right reason to action, which itself presupposes right desire. An inordinate love of honor is therefore opposed to prudence, because it involves an inordinate desire. Furthermore, prudence presupposes humility [2], which involves knowing the actual limits of your strengths and qualities (it is not the denial of the strengths and qualities you actual have, which is opposed to humility and a common misconception!). Humility allows us to moderate our desires. In that sense, ambition as an inordinate desire for honors beyond one’s reach lacks humility.

[0] https://www.newadvent.org/cathen/01381d.htm

[1] https://www.newadvent.org/summa/3138.htm#article2

[2] https://www.newadvent.org/cathen/07543b.htm

[3] https://www.newadvent.org/cathen/12517b.htm