noun
work day; working day
Refers to a day on which one works, as opposed to a day off. Often used in scheduling or contrasting with holidays.
明日は仕事日だから早く寝ます。
Tomorrow is a work day, so I'll go to bed early.
今週の仕事日は月曜から金曜までです。
This week's work days are Monday through Friday.
平日 means 'weekday', which is a work day for most people, but 仕事日 can refer to any scheduled work day, including weekends.
Compound of 仕事 (shigoto, 'work') and 日 (hi, 'day'), with rendaku voicing hi → bi.