Good Evening
expression
This word is made of now and night with the hiragana は at the end. The は here is pronounced as わ (the old pronunciation). When you say "now night!" you're really saying good evening.
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. Just be aware that the は at the end is actually the particle は so it's pronounced like わ.
今晩は。こんな所で何してるの？
Good evening. What are you doing in a place like this?
「あ、今晩は。」「今晩は。昨日の社長とのミーティング、どうだった？」
"Oh hey, good evening." "Good evening. How was the meeting with the president yesterday?"
今晩は家でゆっくり映画でも見るつもりです。
Tonight, I plan to relax at home and watch a movie.