Learn English – the difference between “turn off” and “switch off”

Please note that this is not based on any cited source but on my own observations.

Colloquia and seminars both happen in an academic setting. At my university we have a weekly physics colloquium that — in general — is geared to a well educated, but not specialized audience. (I.e., a particle physicist will present a topic on a fairly advanced level, but so that, say, a condensed matter physicist will still be able to understand). In general they seem to be more "populist" and less technical, covering popular topics in physics (quantum information, graphene) and in the news (global warming, nuclear weapons/power) but from the perspective of a scientist.

A seminar on the other hand, in an academic setting, is a much more specialized meeting, also with a formal academic presentation. For instance, there are weekly seminar meeting for the Atomic, Particle, String Theory, Condensed Matter, and Astrophysics groups. There is also an invited speaker, but the audience is much more technically versed and the topics tend to be much more technical or specific to the field. Generally someone from outside the field will have trouble understanding a seminar presentation.

In a grand sense the two words are equivalent, but a colloquium, as pointed out, is literally a "conversation" and in general has a connotation of being more broad, more accessible, or on a more popular topic.

Peasant and villager are not completely synonymous. While a villager is just someone who lives in or comes from a village, peasant is more likely to be used in a pejorative way:

1. (especially in the past, or in poorer countries) a farmer who owns or rents a small piece of land
2. (informal, disapproving) a person who is rude, behaves badly, or has little education

A peasant might be described as of low social status, or uncouth, similar to a peon, serf, churl, boor, lout. Closer to villager are synonyms like yokel, bumpkin; but these still imply judgment or disapproval.

Villager alone lacks such a strong negative connotation. It could be used to describe someone from a village without obvious reference to their profession and without implying that they're ignorant or from the "back woods", though there are often assumptions that life in villages matches stereotypes such as being simpler, more authentic, or less modern: The villagers adjusted well after moving to the big city.

Interestingly, the etymology of both words reflects that they describe people from a physical location. Peasant is from Latin pagus "country or rural district"; villager is from Latin villa "country house, farm".