Difficult; hard; troublesome; complicated — used for tasks, problems, or serious conditions.
この問題は考えれば考えるほど難しい。
The more I think about this problem, the more difficult it becomes.
彼の説明は分かりにくくて難しい。
His explanation is hard to understand and confusing.
この手術は技術的に難しいと医者が言った。
The doctor said this operation is technically difficult.
Euphemistic: impossible or unfeasible — a softer way to say something can't be done (softer than 'muri').
来週までに全部仕上げるのは難しいです。
It's unlikely I'll be able to finish everything by next week.
その条件で契約するのは難しいと思います。
I think it's difficult (i.e., unlikely) to sign a contract under those terms.
Fussy; particular; hard to please — describing a person who is picky or hard to satisfy.
彼は食べ物に関して難しい人だ。好き嫌いが多い。
He's fussy about food; he has many likes and dislikes.
あの顧客は注文が難しいので、対応に時間がかかる。
That customer is picky, so handling them takes time.
難しい人相手でも落ち着いて話すといい。
Even with a difficult person, it's good to speak calmly.
Gloomy; glum; serious-looking — describing an unpleasant or severe expression or atmosphere.
今日は部長の顔が難しい。何かあったのだろうか。
The manager looks gloomy today. I wonder if something happened.
難しい表情で黙っている彼を見て、気まずくなった。
Seeing him silent with a serious expression made things awkward.
Archaic: dirty; unclean; filthy — an old usage rarely used in modern Japanese.
古い文学作品には「難しい」が『汚らわしい』の意で用いられる部分がある。
In old literature, 'muzukashii' is sometimes used to mean 'filthy' or 'disgusting'.
Archaic: unpleasant; uncomfortable; creepy — an old sense seldom seen in modern usage.
古文の注釈に、『難しい』はここでは「気味が悪い」と説明されている。
A commentary on a classical text explains that here 'muzukashii' means 'creepy'.