flush against

Tuesdays with Morrieも終わりに近くなってきました。ALSのMorrieの容態は悪くなる一方です。
Morrie, dressed in pajama bottoms, lay in bed on his side, his head flush against the pillow, his mouth open. The physical therapist was showing me how to bang loose the poison in his lungs--which he needed done regularly now, to keep it from solidifying, to keep him breathing.
"flush against" の状態が分かりません。 "flush" に私の知らない意味があるに違いありません。辞書を見ます。
・Macmillan Dictionary: if two surfaces or edges are flush, they are exactly level with each other: The cabinet doors aren't quite flush.
・Cambridge English Dictionary: at the same level as another surface: I want the light fittings to be flush with the ceiling.
"flush" も色々な意味を持っているのですね。
Your face can flush, and the sky can flush at sunset when it glows with shades of pink. You can also use flush as an adjective to mean "lined up" or "level," like when you hang a medicine cabinet in your bathroom, making sure it's flush against the wall. Yet another meaning of a flush is a peak or boom ? a professional poker player might describe her period of winning game after game as a flush.(Vocabulary.com)