This is the 547th most frequent Lithuanian word.
didelių
"Didelių" means "big" or "large" (genitive or plural form in Lithuanian).
Here, 'didelių' is used as an attributive adjective in the genitive plural form matching 'svajonių' (dreams).
Jis turi didelių svajonių.
He has big dreams.
In this sentence, 'didelių' modifies 'sprendimų' (decisions), also in genitive plural.
Nepriėmiau didelių sprendimų.
I did not make big decisions.
'Didelių' describes 'išlaidų' (expenses), again as an adjective in the genitive plural case.