Mid 17th century; earliest use found in William Whately (1583–1639), Church of England clergyman and puritan preacher. From un- + purposedly, after unpurposed.
Definition of unpurposedly in US English:
unpurposedly
adverb(ˌ)ʌnˈpəːpəstli
rare
Not purposefully; without purpose.
Origin
Mid 17th century; earliest use found in William Whately (1583–1639), Church of England clergyman and puritan preacher. From un- + purposedly, after unpurposed.