half eaten は「半分食べられた」という意味です。
「飲みかけ」をhalf drunkと言ってしまうと、「半分酔っている」と思われてしまうかもしれません。飲み物の場合は、halfway drunk と言うといいと思います。halfway は「半分の地点にいる」「途中の状態」と言う意味です。
（食べかけのお菓子が目の前にある状態で）例文
Are you going to finish that half eaten sandwich?
「その食べかけのサンドイッチ最後まで食べるの？」
Yeah, I'm still working on it.
「うん。今食べてるところ」
※working on it
訳すと、「まだ取込中」という意味なので、まだ物事の途中であることを表します。
"Half eaten."
This probably the best expression to use in order to describe food/drink partially gone. You also have to remember that it depends on the situation. For example if you are eating a sandwich and you get up to get something to drink, you are not really done wiht your sandwich you are just getting someting to drink therefore its half eaten. Now if you are eating a sandwich and at the half point you are full and no longer want the sandwich then its called leftover because it's what is left over of the sandwich that you no longer plan to eat.
It may be a surprise, or even alarming to notice that someone has been eating or drinking something of yours. It is like the children's story of 'Goldilocks And The Three Bears' when the bears find that their porridge has been interfered with. If someone 'had a go' at your food, it means they have eaten some of it.
あなたの食べかけや飲みかけを誰かが食べたり、飲んだりしていたら驚くことでしょう。「ゴールディロックスと3匹のくま」の話の中の、くまの家族が自分たちの食べかけのおかゆが食べられていたのを見つけたときのようです。 'had a go' とは、少し食べてしまったという意味です。
When you have food left over and are keeping it, you can call them "leftovers". For example, "I'm full. I couldn't finish my dinner. I'll have my leftovers in the morning."
Another example, when you're at a restaurant and do not finish your food, you can ask for a doggy bag.
E.g. I took a doggy bag because I couldn't finish my steak. It was too big to finish.
残りの食べ物を取り置きしているものを"leftovers"（料理の食べ残り/あまり）と呼ぶことが出来ます。
【例】
"I'm full. I couldn't finish my dinner. I'll have my leftovers in the morning."
（お腹が一杯。晩御飯を前夫食べることが出来なかったから、明日の朝の残りを食べます）
もう一つの例です。
レストランで料理を全部食べきれなかった場合 "doggy bag"（お持ち帰り）をお願いすることが出来ます。
【例】
"I took a doggy bag because I couldn't finish my steak. It was too big to finish."
（このステーキは大きすぎて食べきれなかったので、お持ち帰りにする事にしました）
If you have a dish/meal that is not all been eaten then you could say that the meal/dish is 'Half eaten' if you have eaten half of a meal and there is some left you would call whats left 'leftovers' meaning it is what is left-over from the original meal
Someone ate part of my food
This refers to food that only has half of it remaining. The food is no longer whole or full as it was in the beginning.
A part of the food has already been eaten
This expression is used for food which clearly has a missing part or portion. The missing part could consist of anything in the meal: some of the meat, or maybe the rice.
A large chunk of the food has been eaten
This statement can be used to describe a meal which is now unlikely to leave you feeling full as much of it has already been consumed.
Someone ate part of my food（誰かが私の料理を食べた）
- これは、食べかけの食べ物を表します。最初のように完全な形ではないということです。
A part of the food has already been eaten.（料理の一部が既に食べられている）
- これは、明らかに料理の一部が欠けている場合に使います。欠けているのは肉かもしれませんし、ご飯かもしれません。何が欠けていても使えます。
A large chunk of the food has been eaten（料理の大部分が食べられている）
- これは、大部分が食べられた食事を表します。たぶん満腹になりません。
When somebody has ordered or made food or a drink but not finished the whole meal or beverage, wether they are full up and no longer hungry/ thirsty. If this happened at a restaurant you could ask for your food to be packaged up for you to take home and finish later.
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