
If you have questions about the conjugation of дефиниция or Russian nouns in general, you can practice and get feedback from a professional tutor.
Но ты считал, что за людьми на твоей картине не наблюдают, поскольку это - дефиниция актёра.
But you have pretended that the people in your painting are not being watched. Which is the definition of an actor?
- У слова "хорошо" переменчивые дефиниции, мне не подходит.
And "fine" has variable definitions. "Fine" is unacceptable.