Well, when we say community, we refer to a large number of people or entities, who may be affiliated to many smaller or disparate sub-structures.Community almost always refers to a varied and large audience, yet with certain things, which maybe certain interests, opinions, or religion or ethnicity.
On the other hand, group is indeed most often used for a small number of people or other entities, each of which may or may not be large. Also, a group is not as natural a collection as community. A group maybe formed by some of us just now, but a community arises on its own and comes together, and has more naturally common attributes. Similarly, one can be expelled from a group, if he disrespects the rules, but one cannot be banned from a community per se, unless it is something very artificial like a virtual social networking aggregate that is moderated etc.
E.g. we talk about the international community of researchers of a certain field, say Physics, or the international community of institutional investors (each of which is an institution like a bank and consists of millions of people), whereas we say G8- a group of nations.
What about namely?
Assume that this is not true, namely, that there are counterexamples X and Y such that the statements Y < X and X < 2Y are false.
Assume that this is not true--namely, that there are counterexamples X and Y such that the statements Y < X and X < 2Y are false.
Some recommend you use a dash if a comma comes after "namely," but I think it's redundant since the dash signifies namely.
Best Answer
I don't think "sounds more/less professional" is really a relevant factor here.
There are contexts where we always use derivatives of manufacture rather than make (for example, companies may have their manufacturing plants, but never their making plants).
But when it comes to describing companies that produce X's, the main thing that affects whether we call them X makers or X manufacturers is the complexity/scale of the production process.
Have a look at these charts for furniture, car, television, and aircraft. In that sequence, they show an increasing preference for manufacturer, which I think reflects our perception of complexity.
As implied by @rsegal's comment, maker (as a much older word) has stronger associations with "pre-industrialised" production (on a smaller scale, more "custom-built" products, etc.).
But these are just usage tendencies - there's no definitive rule in play. FWIW, there are 2-3 times as many piston manufacturers as there are piston makers, but I very much doubt there would be any tendency at all for the latter to be either smaller, or "less professional" companies.
To the extent that we might choose one word over another, our choice is governed by the product and/or the processes involved, not by attributes of the company that produces them.