ae·ci·um (??s?-?m, ??sh?-)n. pl. ae·ci·a (-s?-?, -sh?-?) A cuplike structure of some rust fungi that contains chains of aeciospores.[New Latin, from Greek aiki?, injury, from aik?s, unseemly, injurious : a-, not; see a-1 + eikenai, to seem, be seemly.]ae?ci·al (??s?-?l, -sh?-) adj.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.aecium (?i?s??m) or aecidiumn, pl -cia (-s??) or -cidia (-?s?d??) (Botany) a globular or cup-shaped structure in some rust fungi in which aeciospores are produced[C19: New Latin, from Greek aikia injury (so called because of the damage the fungi cause)]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014ae?ci?um (?i si ?m, ?i ?i-) n., pl. ae?ci?a (?i si ?, ?i ?i ?) the fruiting body of rust fungi, which bears chainlike or stalked spores. [