Source : Webster's Revised Unabridged Dictionary (1913)

Workday \Work"day`\, n. & a. [AS. weorcd[ae]g.]
   A day on which work is performed, as distinguished from
   Sunday, festivals, etc., a working day.

Source : WordNet®

workday
     n 1: a day on which work is done [syn: {working day}, {work day}]
          [ant: {rest day}]
     2: the amount of time that a worker must work for an agreed
        daily wage; "they work an 8-hour day" [syn: {working day}]