From Longman Dictionary of Contemporary Englishhalf dayˈhalf day, half-day noun [countable] HOLIDAYa day when you work or go to school either in the morning or the afternoon, but not all day Friday is my half day off.
Examples from the Corpus
half day• Until then, I, like many parents, thought there were two choices: half day or full day.• She probably has one half day free per week, and then she will have to visit her parents, no doubt.half-dayˈhalf-day adjective [only before noun] a half-day event takes place in either the morning or the afternoon half-day courses on study skillsExamples from the Corpus
half-day• The half-day course on the Census introduces the problems but does not attempt to discuss them in depth.• The half-day courses include two hours practical experience of firing and driving with full instruction on safety and how the engine works.• Cost is $ 40 per person for the half-day excursions, and $ 70 for a full day, including lunch.• In half-day kindergarten programs, school districts need only half the number of kindergarten teachers and kindergarten classrooms.• Both the advantages and disadvantages of the half-day kindergarten seem to circle around the issues of time and expense.• As I said before, I could go to half-day school here.• Jurors resume their deliberations today after a half-day session Friday.• This was usually in the form of one day or two half-day sessions. 