The American Heritage Dictionary of the English Language, Fourth Edition, gives one definition of the verb mark as "to evaluate (academic work) according to a scale of letters or numbers; grade." In this sense a grading system and a marking system are equivalent. Similarly, in the United States you will hear regional variations where a grading period in one area is the same as a marking period elsewhere.
But the verb point is not synonymous with the verb grade. So a pointing system is not the same as a grading system.
However, the noun point is synonymous with the noun grade. From the same dictionary, one of the definitions of the noun point is "a numerical unit of academic achievement equal to a letter grade." Similarly, the noun mark is defined as "a number, letter, or symbol used to indicate various grades of academic achievement."
Therefore, grade, mark, and point are synonyms when used as nouns. But only grade and mark are synonyms when used as verbs.
Note that could is the past form of can, and might is the past form of may.
Past forms of these words are used in subjunctive and conditional constructions.
I can go to the cinema is a statement that you are able to go without any external conditions being in the way. (But the statement stops short of making a commitment: namely that you will go to the cinema.)
I could go the cinema. has multiple interpretations. One is that it's an incomplete conditional thought. You could go to the cinema, if what? It can also be uttered by someone who is in the middle of making a decision. What should I do tonight? Hmm, I could go to the cinema.
Quite possibly, in this kind of reasoning, the speaker, to some extent, externalizes the internal conditions on which the decision hinges. It is not simply true that the speaker can go to the cinema, because that is only possible if he doesn't choose some other mutually exclusive activity for the evening which precludes going to the cinema. That may be semantic the basis for why the conditional-making past participle is used for such statements.
I could go to the cinema tonight or I could go clubbing. I know! If I catch an early movie I can go to the cinema and I can go clubbing.
Now about may. I may go to the cinema is very similar to I can go the cinema, but as a native speaker, you know the difference between can and may being that between ability and permission or possibility.
Furthermore, modern English, the semantics of can stretches to cover that of may (but only in the area of permission, rather than possibility). Children frequently ask grownups permission using can I rather than may I.
I may go to the cinema has at least two possible meanings. One is that the speaker's privilege for that outing depends on permission from some authority. I can go to the cinema can still imply that, depending on the context. For instance, it obviously does in My dad said I can go to the cinema tonight.
But I may go to the cinema also has another meaning: that of possibility, and it means that going to the cinema is on the speaker's short list of possible activities. If an adult states that he or she may go to the cinema, of course we assume this interpretation, and not that the adult has permission from someone else. And I might go to the cinema means approximately the same thing.
The difference between I could go the cinema and I might/may go to the cinema is that the former is associated with reasoning about conditions or alternatives, whereas the latter is just a statement of possibility. The former statement informs us about a decision-making process going on inside the speaker, whereas the latter statement informs us that it is possible that the speaker will later be found at the cinema.
Something might happen and something may happen are not exactly the same, because might is used when conditions are attached. For example, if you lean over the rail, you might fall is more correct than if you lean over the rail, you may fall because you may fall states a possibility which is not conditional on anything. The verb might can substitute for may in expressing a pure unconditional possibility, but the reverse isn't true.
Best Answer
This is one of the cases where English has a bunch of words that mean very nearly the same thing because of its many overlaid mass borrowings from its neighbors, and in this case also because of the rich and ancient tradition of warfare in Europe. If you pick the wrong word, native speakers will still understand, but they may get slightly the wrong impression. Don't worry about it too much.
I'm going to explain the words in a slightly different order than you listed them.
A fortification is any structure whose primary function is to aid a military defense. It is most often used for structures whose only function is defense, such as city walls, trenches, tank barriers, etc. Fortifications might not be permanent structures; the trenches of World War I were dug as needed and filled in when no longer useful. There's a related verb: you fortify something when you prepare to defend it (not necessarily by erecting fortifications). This term is in current usage.
A fort is a building or group of buildings designed to serve as a base for an army. It also serves as a fortification in the above sense; it may for instance have artillery emplacements, walls designed to resist cannonfire, etc. This term is also current, but is fading out of the language in favor of "[military] base", partly because traditional fortifications are less and less useful in modern warfare. Forts often have names: "Fort Pitt", for instance, is the name of a fort (built in the 1730s and now almost entirely gone) near where I live.
Fortress, castle, citadel, and stronghold are all roughly synonymous with fort. There are, however, differences of nuance:
Finally, a palace is the home of a monarch or other high-ranking feudal lord (a duke or a prince, perhaps). It is not necessarily a castle, and in fact often deliberately not a defensible fort (consider Versailles). By extension it is sometimes used to refer to any large, ostentatious, expensive dwelling. This word is in current usage.
Etymologically, fort, fortress, and fortification are all from the French root fort = [place of] strength; palace and citadel are also from Norman French palais, citadelle; castle was borrowed directly from Latin castellum and then reinforced by Norman French castel (which became château in Modern French); and stronghold is Old English, a composition of strong + hold.
Other related words include: