chlorthalidone (kl????æl?d??n) n (Pharmacology) a diuretic used in the treatment of congestive heart failure and hypertension[C20: from chlor(o)- + th(iazine) + -al3 + -id(e) + -one]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014