The Collaborative International Dictionary of English v.0.48:

Silverboom \Sil"ver*boom`\, n. [D. zilver silver + boom tree.]
   (Bot.)
   See Leucadendron.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Leucadendron \Leu`ca*den"dron\ (l[=u]`k[.a]*d[e^]n"dr[o^]n), n.
   [NL., fr. Gr. leyko`s white + de`ndron tree.] (Bot.)
   A genus of evergreen shrubs from the Cape of Good Hope,
   having handsome foliage. Leucadendron argenteum is the
   silverboom of the colonists.
   [1913 Webster]