[ Source for English law : ] Adverse Possession means someone occupying land belonging to someone else, without permission. If someone does this continuously for a number of years (normally 10 or 12 years) then, in certain circumstances, the land may become theirs.
[ US Source : ] Adverse possession is a doctrine under which a person in possession of land owned by someone else may acquire valid title to it, so long as certain common law requirements are met, and the adverse possessor is in possession for a sufficient period of time, as defined by a statute of limitations.
I already understand, and so ask not for, the definition. Instead: what motivated the use of adverse to describe the legal notion? What semantic notions underlie the prosaic and the legal meanings?