I am here to referring to comes in its governmental context, not as a word meaning companion.
I have seen the word comes used both as a rank and as a job. For example, Wikipedia mentions that "Constantine created a third order of nobility, the comites..." This makes it seem that comes was a rank, like Colonel or Baron.
On the other hand positions like comes rerum privatum (Count of the Private Estates) make it seem that comes was a job, like Secretary of a Department in the US.
So, is comes a (type of) job, or a noble rank?