A Few Days Ago, Other Day
Noun
せんじつ
先日はどうもありがとうございました。
Thank you so much for the other day.
先日いった北かいどうのおまつりは二十日かんもつづくものらしい。
I heard that the festival I went to the other day in Hokkaido is held for twenty days.
彼女は先日からずっと病気で寝ていると嘘をついた。
She was lying about being sick in bed for a few days.
The previous day isn't necessarily yesterday. It can be any recent day, which is why this word means the other day.
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. Note that the 日 reading is the alternate reading, じつ.