@pettter You could theoretically get noncapitalist colonialism, e.g. if a monarch extracted resources for the monarchy – arguably what Leopold did in the Congo could fall under that, but he was kinda enriching himself personally rather than the institution of monarchy, so I think the possibility remains theoretical.
The difference with empires seems much clearer to me – they usually describe collections of states, rather than single states. There might be a single state at the center of the empire, but the imperial core might consist of multiple states as well. This is a pretty fuzzy category though – I could see the American Empire as having the core in the US and a lot of peripheral countries under it’s (partial) control, or a Western Empire, where the core consists of the US+Europe+Canada+Australia (and perhaps some other’s I forgot), with various degrees of “coreness” for different states. In the first case you could look at Europe as a soft periphery of the American Empire, or as a core of its own European Empire. I think these are lenses for analysis rather than strict descriptions of reality. Oh, and I’m definitely not trying to imply these are the only contemporary empires, just examples.
Just a dump of how I tend to use the term, not sure if that’s in any way a useful answer for you.