The Collaborative International Dictionary of English v.0.48:

Haustellum \Haus*tel"lum\ (h[add]s*t[e^]l"l[u^]m), n.; pl.
   Haustella (-l[.a]). [NL.] (Zool.)
   The sucking proboscis of various insects. See Lepidoptera,
   and Diptera.
   [1913 Webster]