To Extend
To Spread
intransitive verb, godan verb
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means extend so the verb vocab version is to extend.
Does the kanji look familiar, kind of like 広い, perhaps? 拡がる is the less common and narrower counterpart of 広がる. It's used to describe the enlargement or extension of the size, area, or range of something.
This word shares the same reading as 広い. That means 拡がる is read as ひろがる.
薄暗い部屋の床に、血が静かに拡がっていた。
Blood was silently spreading on the floor in a dim room.