The Collaborative International Dictionary of English v.0.48:

Tous-les-mois \Tous`-les`-mois"\, n. [F., all the months, i. e.,
   every month.]
   A kind of starch with very large, oval, flattened grains,
   often sold as arrowroot, and extensively used for
   adulterating cocoa. It is made from the rootstocks of a
   species of Canna, probably Canna edulis, the tubers of
   which are edible every month in the year.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Canna edulis
    n 1: canna grown especially for its edible rootstock from which
         arrowroot starch is obtained [syn: achira, indian shot,
         arrowroot, Canna indica, Canna edulis]