As much as I know the prefix dis mostly means – no, stop, and the opposite.
In such words like: dislike – stop liking, disrespect – no respect, disconnect – the opposite for connect.
But in such words like: discover, discuss, disguise, display what does "dis" mean? Or maybe it isn't a prefix in these words?
Best Answer
While I am inclined to agree with fixer1234's comment, having done a bit of research on all the words you mention it seems that all of them lead back to origins with dis/des prefixes. It's just some of these words have taken a few detours in definition which don't make that connection as clear as some of the words you mentioned earlier.
For discover, the word originates from the Late latin discooperire, which breaks down into dis (opposite of) and cooperire (to cover up), as Trent mentions in his comment above.
For discuss, the word originates from the Latin discutere, which breaks down into dis (apart) and quatere (to shake). It seems that the definition shifted from smashing apart to scatter or disperse, then to investigate or examine and finally to debate.
For disguise, the word originates from the Old French desguiser, which breaks down into des (away, off) and guise (style, appearance - a word we still use today).
For display, the word originates from the Latin displicare, which breaks down into dis (apart) and plicare (to fold). This definition was used with regards to sails and flags (the idea of unfurling them/revealing them) and has gradually morphed to what it is today.