Alternative form of if one is a day

Ordinary or mundane. / Happening every day. / (US, sports) Subject to daily redetermination.

On a daily basis.

Ordinary, monotonous routine; that which is usual or mundane.

Alternative spelling of day-to-day

(idiomatic) A particularly noteworthy day; the day on which a milestone or especially memorable event occurs. / (Christianity, sometimes capitalized) Sunday, especially Easter Sunday.

Alternative form of day of days

one day at a time / gradually

plural of day of days

Any period of 24 hours. / A period from midnight to the following midnight. / (astronomy) Rotational period of a planet (especially Earth).