rhizome
Concise Oxford English Dictionary © 2008 Oxford University Press:
rhizome /ˈrʌɪzəʊm/
▶noun Botany a continuously growing horizontal underground stem with lateral shoots and adventitious roots at intervals.
– origin C19: from Gk rhizōma, from rhizousthai ‘take root’, based on rhiza ‘root’.
'rhizome' also found in these Oxford entries:

