opposite, apposite

Opposite or opposite means contrary or radically different; the reverse or inverse--
We told him to drive west, but he went in the opposite direction.
The opposite of hot is cold.

Apposite or apposite means relelvant or suitable; apt--
His reply was somewhat rude, but apposite.
He seemed to digress, but in the end his remarks were apposite.

Now that you know that, you can say--
"The opposite of apposite is irrelevant."

Note--"oppose it" ( two words ) means to  resist, combat, or act against ( oppose ) something ( it)--
Do you think he will support the measure, or oppose it?

Note # 2--"a posit" ( two words ) means one ( a ) assumption or postulate ( posit )--
If we can agree on a posit, we can begin our argument from there.

Note # 3--"op cit" is used in footnotes, an abbreviation of the Latin opere citato, meaning "in the work cited"--
See Chapter VII, op. cit.