ham·a·dry·ad 
(hăm′ə-drīəd)
(hăm′ə-drīəd)n. pl. ham·a·dry·ads or ham·a·dry·a·des (-ə-dēz′)
1. Greek & Roman Mythology A wood nymph who lives only as long as the tree of which she is the spirit lives.
2. See king cobra.
[Middle English amadriad, from Latin Hamadryas, Hamadryad-, from Greek Hamadruas : hama, together with; see sem-1 in the Appendix of Indo-European roots + Druas, dryad (from drūs, oak; see deru- in the Appendix of Indo-European roots).]