almost every day; constantly
Fixed expression meaning something happens so frequently that not even three days pass between occurrences. Often used with verbs of occurrence or action.
See also: 三日にあげず
He goes to the library almost every day.
この店には三日と上げず新しい商品が並ぶ。
New products appear in this store almost every day.
Standard kanji-kana mixed spelling.
Kana spelling of 上げ; common in everyday writing.
From 三日 (three days) + と (quotative particle) + 上げず (negative of 上げる, here meaning 'to pass'). Literally 'without letting three days pass', i.e., something occurs so frequently that not even three days go by without it.