This is the 14589th most frequent Russian word.
первоначальных
"Initial" or "original."
In this sentence, 'первоначальных' acts as an adjective in plural form, modifying the noun 'идей' (ideas), referring to the 'original' or 'initial' ideas.
Он вернулся к первоначальных идеям своего проекта.
He returned to the original ideas of his project.
Here, 'первоначальных' describes 'планов' (plans) and conveys the meaning of 'original' or 'initial' plans that existed prior to changes.
Её первоначальных планов изменили обстоятельства.
Her original plans were changed by circumstances.
The adjective 'первоначальных' pertains to 'попыток' (attempts), implying 'early' or 'initial' efforts.