ˈhalf day ,
half-day noun [countable] a 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. [TahlilGaran] Dictionary of Contemporary English ▲
ˈhalf-day adjective [only before noun] a half-day event takes place in either the morning or the afternoon:
half-day courses on study skills [TahlilGaran] Dictionary of Contemporary English ▲