noun, adverb
Often used as a shorter form of 一週間, especially in compounds or when the context makes the time unit clear. Can function as a noun or adverbially.
See also: 一週間
一週に一度は運動するようにしている。
I try to exercise once a week.
この仕事は一週では終わらない。
This work won't be finished in one week.
一週間 is the full, explicit form meaning 'one week' and is more common in standalone use. 一週 is a shorter variant often used in compounds or when the time unit is understood.
Compound of 一 (one) and 週 (week). The reading いっしゅう results from the regular sound change of 一 (いち) before an unvoiced consonant.