“sad” is a basic word. You say it in some situations in daily conversation. I will introduce how you can translate it in Japanese, what sieciatuation you can use it in and the surrounding knowledge.
You can translate “sad” into “kanashii”/「悲しい」to express your feelings in many cases. If you stay in Japan and know that there is no problem.
My dog has passed away, so I’m sad now./犬が亡くなって、今とても悲しいです。
“kanashii”/「悲しい」in Japanese has some nuances. So on the contrary there are some expressions in English with the meanis of “kanashii”/「悲しい」. It’s better if you learn them.
You can translate “kanashii”/「悲しい」into “disappointed” or “heartbroken” in some situations. I will introduce the example.
Is practice for baseball canceled today ? I’m really disappointed./今日の野球の練習は中止になるの？とても悲しいよ。
You can translate “kanashii”/「悲しい」into “unhappy” or “miserable” in some situations. I will introduce the example.
She always writes stories with unhappy endings./彼女はいつも悲しい結末の小説を書きます。
You can also translate “sad” into “hidoi”/「ひどい」in the limited case. In this case you don’t express your feelings, but it means almost the same as “bad”. I will introduce the example.
I made a sad mistake at work./仕事でひどいミスをしてしまった。
If you use “sad” as to color, you can translate it into “jimina”/「地味な」. I will introduce the example.
She likes a sweater with a sad color./彼女は地味なセーターが好きです。
You can translate “sad” into “kanashii”/「悲しい」, “hidoi”/「ひどい」 or “jimina”/「地味な」. You would say “kanashii”/「悲しい」among them in many cases. On the contrary you can translate “kanashii”/「悲しい」 into “disappointed” or “unhappy” in some situations.