mid-14c., sicamour "mulberry-leaved fig tree," from Old French sicamor, sagremore, from Latin sycomorus, from Greek sykomoros "African fig-tree," literally "fig-mulberry," from sykon "fig" (see fig) + moron (see mulberry). But according to many sources this is more likely a folk-etymology of Hebrew shiqmah "mulberry."
A Biblical word, originally used for a wide-spreading shade tree with fig-like fruit (Ficus sycomorus) common in Egypt, Palestine, Syria, etc., whose leaves somewhat resemble those of the mulberry; applied in English from 1580s to a large species of European maple (also plane-tree), perhaps because both it and the Biblical tree were notable for their shadiness (the Holy Family took refuge under a sycamore on the flight to Egypt), and from 1814 to the North American shade tree that also is called a buttonwood, which was introduced to Europe from Virginia 1637 by John Tradescant the Younger).
Spelling apparently influenced by sycamine "black mulberry tree," which is from Greek sykcaminos, which also is mentioned in the Bible (Luke xvii.6). For the sake of clarity, some writers have used the more Hellenic sycomore in reference to the Biblical tree.