half-

prefix

one of two equal partshalf-moon
related by one parent onlyhalf-sister
not completely; partlyhalf-hardy

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for half-

"sharing one parent," from half. Half-brother is attested from early 14c.; half-sister from c.1200.