The Collaborative International Dictionary of English v.0.48:

manna ash \manna ash\ n. (Bot.),
   A South Mediterranean ash (Fraxinus ornus) having fragrant
   white flowers in dense panicles and yielding manna.

   Syn: flowering ash, Fraxinus ornus.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

manna ash
    n 1: southern Mediterranean ash having fragrant white flowers in
         dense panicles and yielding manna [syn: manna ash,
         flowering ash, Fraxinus ornus]