ecological adj.

1873, oecology, "branch of science dealing with the relationship of living things to their environments," coined in German by German zoologist Ernst Haeckel as Ökologie, from Greek oikos "house, dwelling place, habitation" (from PIE root *weik- (1) "clan") + -logia "study of" (see -logy). In use with reference to anti-pollution activities from 1960s.

compound adjectival word-forming element, usually interchangeable with -ic but sometimes with specialized sense (such as historic/historical, politic/political), Middle English, from Late Latin -icalis, from Latin -icus + -alis (see -al (1)). Probably it was needed because the forms in -ic often took on a noun sense (for example physic). Forms in -ical tend to be attested earlier in English than their twins in -ic.