This is the 7365th most frequent Russian word.
гигантскую
The Russian word "гигантскую" means "gigantic" or "huge" in English.
The word 'гигантскую' is used here as an adjective in feminine form to describe the toy as being gigantic.
Она купила гигантскую игрушку для своей собаки.
She bought a gigantic toy for her dog.
In this case, 'гигантскую' is intended as an adjectival form but mismatched syntactically; it should be 'гигантским' or 'гигантское' depending on the noun's case and gender.
Здание на улице выглядит просто гигантскую.
The building on the street looks simply gigantic.
Here, 'гигантскую' functions as an adjective to describe 'проблему' (a feminine noun), emphasizing the massive nature of the problem.