Appropriate
Proper, Suitable, Irresponsible
noun, な adjective
Everything is suitable and right. Therefore it is appropriate, proper, and suitable. Strangely enough, this also means irresponsible. Maybe it's because when everything is suitable and right for you, you're taking too much and not leaving enough for everyone else, making you irresponsible?
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
適当な答えを選んでください。
Please choose the appropriate answer.
あいつは適当な事ばかり言っている。
That guy often says irresponsible things.
居酒屋で、同僚が店員に「適当にお願いします」と言って注文をしたことに驚きました。
I was surprised when my colleague was ordering in an izakaya and said to the waitress: "Choose whatever you think is best".