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Webster 1913 Edition
Aaron's rod
Aar′on’s rodˊ
(âr′ŭnz rŏdˊ)
. [See Exodus vii. 9 and Numbers xvii. 8] 
1. 
(Arch.) 
A rod with one serpent twined around it, thus differing from the caduceus of Mercury, which has two. 
2. 
(Bot.) 
A plant with a tall flowering stem; esp. the great mullein, or hag-taper, and the golden-rod.