Zannichellia palustris zan·nic·hel·liapalustris uncommon noun 1. found in still or slow-moving fresh or brackish water; useful to oxygenate cool water ponds and aquaria Synonymshorned pondweedZannichellia palustris Related words Broader terms pondweed WordNet 2.1 (Princeton University). WordNet 2.1 Copyright Princeton University. All rights reserved.