iron tree
/ˈʌɪən ˌtriː/noun
Any of several trees and shrubs yielding very hard heavy wood; specifically (a) Mesua ferrea (family Calophyllaceae), native to Sri Lanka and introduced in parts of South-East Asia; (b) Caesalpinia ferrea (family Caesalpiniaceae (Leguminosae)) of Brazil and other parts of South America.
Origin
Early 17th century. From iron + tree, so called on account of the hardness of the timber and also on account of its weight.