dissepiment
Concise Oxford English Dictionary © 2008 Oxford University Press:
dissepiment /dɪˈsɛpɪm(ə)nt/
▶noun Botany & Zoology a partition in a part or organ; a septum.
– origin C18: from L. dissaepimentum, from dissaepire ‘make separate’.
'dissepiment' also found in these Oxford entries:

