A quick glance at the questions tagged display showed at least (3) talking about the UI of an application, (2) talking about HDTVs, (2) talking about laptop screens (not normally referred to as "monitors"), and at least (1) talking about projectors.
"Display" is definitely not being used consistently as a synonym for "monitor".
I had a look at these questions. display and monitor should remain separate tags as in most cases they are not used as synonyms, and where they are there is enough users with tag editing power to fix the anomalies.
Where display and monitor is used, the most relevant one must be chosen and applied. I have gone through these and re-tagged so they should not be there.