Suitable; appropriate; proper — fitting for the situation or purpose.
会議の時間は目的に適当な長さに調整してください。
Please adjust the meeting time to a length appropriate for the purpose.
その仕事には彼が適当だと思う。
I think he is suitable for that job.
適当な服装でお越しください（フォーマル／カジュアルなど指示あり）。
Please come in appropriate attire (there may be guidance like formal/casual).
Perfunctory; careless; sloppy — done without care or commitment (colloquially 「テキトー」).
仕事をテキトーにやると、後で大きな問題になる。
If you do work sloppily, it will become a big problem later.
あの人は約束を守らないし、いつも適当だ。
That person doesn't keep promises and is always unreliable/sloppy.
説明が適当すぎて、質問がたくさん出た。
The explanation was too cursory, and many questions came up.