From The Collaborative International Dictionary of English v.0.48 :
Tmesis \Tme"sis\ (m[=e]"s[i^]s or t'm[=e]"s[i^]s; 277), n. [L.,
from Gr. tmh^sis a cutting, fr. te`mnein to cut.] (Gram.)
The separation of the parts of a compound word by the
intervention of one or more words; as, in what place soever,
for whatsoever place.
[1913 Webster]