Mid 19th century; earliest use found in Chemist. From allo- + -tropic + -al, ultimately after Swedish allotropisk: see slightly earlier allotropic and foreign-language forms cited at that entry.
Definition of allotropical in US English:
allotropical
adjectiveˌaləˈtrɒpɪkl
Chemistry
Allotropic.
Origin
Mid 19th century; earliest use found in Chemist. From allo- + -tropic + -al, ultimately after Swedish allotropisk: see slightly earlier allotropic and foreign-language forms cited at that entry.