Verb
splain (third-person singular simple present splains, present participle splaining, simple past and past participle splained)
(informal, dialectal) Aphetic form of explain.
splain (third-person singular simple present splains, present participle splaining, simple past and past participle splained)
(slang) To condescendingly explain something, often extensively, especially to someone that knows more about it; for example, to mansplain, whitesplain, etc.