The Collaborative International Dictionary of English v.0.48:

Mesenchyma \Mes*en"chy*ma\, n. [NL., fr. Gr. me`sos middle +
   -enchyma, as in E. parenchyma.] (Biol.)
   The part of the mesoblast which gives rise to the connective
   tissues and blood.
   [1913 Webster]