adverb
once a week
Colloquial adverb meaning 'once a week'. Often used in casual conversation or informal writing.
このクラブは週一で集まっている。
This club meets once a week.
週一くらいは外食してもいいよね。
It's okay to eat out about once a week, right?
毎週 means 'every week' (regularly), while 週一 specifies the frequency as 'once a week'.
週に一度 is the standard, more formal way to say 'once a week'; 週一 is a colloquial abbreviation.
Abbreviation of 週に一度 (しゅうにいちど, 'once a week'), with 一 (いち) replacing 一度.