The word disharmonious simply means to be out of harmony; in other words, out of tune.
If you add the word spirit to the end it means you have a spirit who is “out of tune” with you. An out of tune spirit has very different energy, or vibrations, than you and wishes ill will upon you rather than good, happy things.
Sometimes demons are referred to as disharmonious spirits, and yes, they too are disharmonious. However, they’re a completely different type of entity.
Personally I try to refer to demons as disharmonious “entities” (it tends to not frighten people as much) and spirits (a soul that was once in a body) who isn’t in sync with the good things in our life, a disharmonious “spirit”.
I hope this little definition helps you better understand the difference between the two.