arboretum
Concise Oxford English Dictionary © 2008 Oxford University Press:
arboretum /ˌɑːbəˈriːtəm/
▶noun (pl. arboretums or arboreta /-tə/) a botanical garden devoted to trees.
– origin C19: from L., ‘a place with trees’, from arbor ‘tree’.
'arboretum' also found in these Oxford entries:

