AIさん、
ご質問どうもありがとうございます。
｛英訳例｝
sleep with one's eyes open
目を開けたまま寝る
｛解説｝
「目を開けたまま寝る」という意味です。
「半開き」の「半」は訳さなくても大丈夫だと思います。
［with A C］は「AをCの状態にして」という意味です。
with one's eyes open で「目を開けたままにして」となります。
｛例｝
He was sleeping with his eyes open.
→彼は目を開けたまま寝ていた。
Rabbits often sleep with their eyes open.
→ウサギはしばしば目を開けたまま寝る。
【出典：Express.co.uk-Jun 18, 2015】
Sometimes he sleeps with his eyes open.
→彼はときどき目を開けたまま寝る。
【出典：Legacy by Robert J. Crane】
He's sleeping with his eyes open.
→彼は目を開けたまま寝ている。
~~~~~~~~~
お役に立てば幸いです。
どうもありがとうございました。
"He was sleeping with his eyes half open."
"She was asleep, but her eyes were ajar."
"He was sleeping with his eyes slightly open."
例：
"""He was sleeping with his eyes half open.""
半開きの目で寝ている。
""She was asleep, but her eyes were ajar.""
彼女は寝ているけど、目が半開きだ。
""He was sleeping with his eyes slightly open."""
彼は、ちょっと目をあけて寝ている。
All of these are examples of how you may describe this situation. Half open or half closed means exactly the same thing. Half shut is an alternative way of saying half closed.
"Look at John!"
"Why, what's he doing?"
"He's fallen asleep reading a book, but look, - his eyes are still half open."
"Weird!"
"I'll take a photo and show him when he wakes up!"
上記は全てこのシチュエーションを表現する例です。half openやhalf closedは全く同じことを表しています。Half shutは、half closedの違う言い方です。
"Look at John!" （ジョンをみて！）
"Why, what's he doing?" （なぜ？彼がなにしているの？）
"He's fallen asleep reading a book, but look, - his eyes are still half open."
（本を読みながら寝てしまったんだけど、見てみて、目が半分開いているんだ。）
"Weird!" （変だね）
"I'll take a photo and show him when he wakes up!" （写真とっておいて後でみせてやろっと）
"Your eyes were half shut/half closed."
This means the person's eyes were not wide open and not closed either.
"Your eyes were open halfway."
This means the person's eyelids were 50% closed and 50% open,
.
"You slept with your eyes partially open."
This means the person's eyes were not completely closed
"Your eyes were half shut/half closed."
これは、その人の目がよく開いてもなければ閉じてもいないときに使います。
"Your eyes were open halfway."
その人の目が50％開いてて、もう半分閉じている時に使います。
.
"You slept with your eyes partially open."
目が一部空いている状態で寝ている人を表します。
This means that this person is trying to sleep and be awake at the same time.
Maybe they are too excited to sleep or afraid of sleeping due to their surroundings.
Shut is the opposite of open.
"The door was open."
"The door was shut/closed."
これは、寝ながら起きるようとしているということを意味します。
多分、とても興奮しているので眠れないかもしれませんし、周りのせいで眠るのを恐れているのかもしれません。
「shut」は開けるの反対語です。
The door was open.
ドアが開きました。
The door was shut/closed.
ドアが閉まりました。
The first sentence is a typical phrase to use in a such situation. But most people use the second sentence due to it being a more casual way of explaning.
"To sleep with eye's slightly open," and, "To sleep with eye's partially open," can be used in the same way as these two examples are only different in terms of the adverb that is used. "Slightly (やや)," describes the verb by saying that it is only done a little bit, which has a very similar meaning to, "partially (部分的に)," as this describes something being done a little bit.
"To sleep with eye's slightly open"（半目を開けて寝る）
と、
"To sleep with eye's partially open"（半目を開けて寝る）
は同じように使うことができます。この二つの違いは副詞だけです。
"Slightly"（やや）は「少しだけ」という意味で、動詞を修飾します。これは "Partially"（部分的に）と非常に意味が似ています。"Partially" も「少し」を表します。
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