The Collaborative International Dictionary of English v.0.48:
Midsummer \Mid"sum`mer\, n. [AS. midsumor.] The middle of summer. --Shak. [1913 Webster] Midsummer daisy (Bot.), the oxeye daisy. [1913 Webster]WordNet (r) 3.0 (2006):
midsummer n 1: June 21, when the sun is at its northernmost point [syn: summer solstice, June 21, midsummer] [ant: winter solstice]