The Collaborative International Dictionary of English v.0.48:
Midweek \Mid"week`\, n. The middle of the week. Also used adjectively. [1913 Webster]WordNet (r) 3.0 (2006):
midweek adv 1: in the middle of the week n 1: the fourth day of the week; the third working day [syn: Wednesday, Midweek, Wed] 2: the middle of a week