This is the 12667th most frequent Polish word.
niedostateczną
"Insufficient" or "failing" (used to describe a grade).
In this context, 'niedostateczną' is used as an adjective in its accusative singular form to describe the grade the student received, qualifying it as unsatisfactory.
Uczeń otrzymał niedostateczną ocenę na sprawdzianie.
The student received an unsatisfactory grade on the test.
Here, 'niedostateczną' functions as an adjective in its accusative singular form to describe an insufficient amount, emphasizing its inadequacy.
Niedostateczną ilość wody może powodować odwodnienie.
An insufficient amount of water can cause dehydration.
In this sentence, 'niedostateczną' is again an adjective in its accusative singular form, modifying 'effort' to highlight its inadequacy as the reason for failures.