-aceae suffix forming plural proper nouns denoting plants belonging to a family: Liliaceae; Ranunculaceae. [New Latin, from Latin, feminine plural of -?ceus -aceous]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014-aceae a suffix used in the formation of names of plant families: Rosaceae. [