This is the 4450th most frequent Russian word.
возможная
Possible.
The word 'возможная' is used as an adjective, modifying the noun 'причина', conveying that the reason being discussed is among those that are considered feasible or plausible.
Это возможная причина её отсутствия.
This is a possible reason for her absence.
Here, the word 'возможная' is implied in the noun form 'возможному', constructed in the dative case to match the sentence's meaning, indicating all feasible options for learning.
Она решила научиться всему возможному.
She decided to learn everything that is possible.
In this case, 'возможные' is an adjective in the plural nominative form, agreeing with 'решения', referring to all solutions that are feasible for the described problem.