rock brake n (Plants) any of various ferns of the genera Pellaea and Cryptogramma, which grow on rocky ground and have sori at the ends of the veins Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014