The OED oppose v. distinguishes two semantic branches for the oppos- group of words, both derived from Latin opponere: Branch I has the senses relating to ‘examination or interrogation’, and Branch II those relating to ‘opposition or opponency’. The former is considered the medieval sense of the word (as a synonym for apposer1), whereas the latter (despite being closer to the Latin core sense) is said to be ‘rare in English before the late 16th century’. The MED supports this statement, with all of the senses of opposen v. falling into the Branch I category. The limited material available in Anglo-Norman, on the other hand, suggests not only that both senses seem to have been attested in medieval times, but also that they cannot be easily separated, with many instances expressing an idea of ‘questioning through objection’ or ‘objecting through questioning’.
For the problematic medical sense (defined on the basis of the Latin source-text), see the note in A-N Med i 265.78.