Where does witch-hazel get its common and botanical names? Is it related to hazel?
You ask a great question, and the answer is confusing. The scientific (botanical) name, Hamamelis comes from the Greek words for ‘together with’ (hama) and ‘fruit’ (melis), according to A Manual of Plant Names, 2nd revised edition, by C. Chicheley Plowden (George Allen & Unwin Ltd., 1970), and it is so called because “the flowers and the fruit are on the tree at the same time.” Or it may be the Greek for “a plant with a pear-shaped fruit, possibly the medlar,” according to William T. Stearn in his Stearn’s Dictionary of Plant Names for Gardeners (Cassell, 1992). Or perhaps ‘melis’ refers to melon, as this page (now archived) from the Holden Arboretum website contends:
“The name Hamamelis is from the Greek hama (together with) and melon (apple or fruit) referring to the fact that the common witch-hazel flowers when the fruit is ripe in fall.”
Whether ‘melis’ refers to fruit, pear-shaped fruit, or melon is not elucidated by An English-Classical Dictionary for the Use of Taxonomists (compiled by Robert S. Woods; Pomona College, 1966), which lists ‘carpos’ for fruit, ‘apioides’ for pear-shaped, and ‘melopepon’ for melon (but meaning apple-shaped, or apple-gourd). The fruit of the witch-hazel is fairly inconspicuous and doesn’t resemble apples, pears, or melons, but one could make a case for its resemblance to medlar.
About the common name, Holden Arboretum says, “Witch is a corruption of wice, Old English for lively or to bend. In Great Britain, a divining rod in the hands of a dowser would become ‘lively’ when it came near an underground water source, pointing to the spot to dig a well. While the ‘witch-hazel tree’ that these divining rods were cut from in England was an elm, Ulmus glabra, American colonists found a suitable replacement in Hamamelis virginiana, which has since been known as a witch-hazel.” Plowden’s book offers an alternate spelling of the common name, ‘wych.’
Hazel is Corylus, which is in the family Betulaceae, while witch-hazel is in the family Hamamelidaceae. I think the connection between witch-hazel and hazel has more to do with a certain similarity of appearance of the leaves.