幾日も幾日も: day after day

the twentieth day of the month / twenty days / Short for 二十日鼠 (hatsuka nezumi): a house mouse

a birthday

one day, 24 hours / the daytime, the period from dawn until dusk / (figuratively) a short period of time / one day, someday, an unspecified day / the first day of the month

regular day off (e.g. closed every Monday)

symmetrical pair, left and right pair

(mahjong) a 役 (yaku, “hand”) of seven pairs, worth 2 翻 (han, “doubles”)

cost-effectiveness, performance or quantity per cost

cost-effectiveness, performance or quantity per cost

(linear algebra) diagonal matrix