The Collaborative International Dictionary of English v.0.48:

Plane \Plane\, n. [F., fr. L. platanus, Gr. ?, fr. ? broad; --
   so called on account of its broad leaves and spreading form.
   See Place, and cf. Platane, Plantain the tree.] (Bot.)
   Any tree of the genus Platanus.
   [1913 Webster]

   Note: The Oriental plane (Platanus orientalis) is a native
         of Asia. It rises with a straight, smooth, branching
         stem to a great height, with palmated leaves, and long
         pendulous peduncles, sustaining several heads of small
         close-sitting flowers. The seeds are downy, and
         collected into round, rough, hard balls. The Occidental
         plane (Platanus occidentalis), which grows to a great
         height, is a native of North America, where it is
         popularly called sycamore, buttonwood, and
         buttonball, names also applied to the California
         species (Platanus racemosa).
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sycamore \Syc"a*more\, n. [L. sycomorus, Gr. ? the fig mulberry;
   ? a fig + ? the black mulberry; or perhaps of Semitic origin:
   cf. F. sycomore. Cf. Mulberry.] (Bot.)
   (a) A large tree (Ficus Sycomorus) allied to the common
       fig. It is found in Egypt and Syria, and is the sycamore,
       or sycamine, of Scripture.
   (b) The American plane tree, or buttonwood.
   (c) A large European species of maple (Acer
       Pseudo-Platanus). [Written sometimes sycomore.]
       [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Buttonwood \But"ton*wood`\, n. (Bot.)
   The Platanus occidentalis, or American plane tree, a large
   tree, producing rough balls, from which it is named; --
   called also buttonball tree, and, in some parts of the
   United States, sycamore. The California buttonwood is
   Platanus racemosa.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sycamore
    n 1: variably colored and sometimes variegated hard tough
         elastic wood of a sycamore tree [syn: sycamore,
         lacewood]
    2: any of several trees of the genus Platanus having thin pale
       bark that scales off in small plates and lobed leaves and
       ball-shaped heads of fruits [syn: plane tree, sycamore,
       platan]
    3: Eurasian maple tree with pale grey bark that peels in flakes
       like that of a sycamore tree; leaves with five ovate lobes
       yellow in autumn [syn: sycamore, great maple, scottish
       maple, Acer pseudoplatanus]
    4: thick-branched wide-spreading tree of Africa and adjacent
       southwestern Asia often buttressed with branches rising from
       near the ground; produces cluster of edible but inferior figs
       on short leafless twigs; the biblical sycamore [syn:
       sycamore, sycamore fig, mulberry fig, Ficus
       sycomorus]