Apocalypse means "revelation" in Greek, from Greek καλύπτω (kalupto) "hide" and ἀπό- (apo-) "un-". It was so used in the New Testament: the last book is called Ἀποκάλυψις Ἰωάννου in Greek, Revelation of John, in which the Last Judgement is revealed to John, the time when the Christian God will end human existence as we know it. From this, apocalypse gained its secondary modern sense of armageddon, the end of the world by the forces of nature or God. In this way it is now most often used. It now means a disaster so great that it will probably destroy most of mankind, and possibly the entire universe.
Cataclysm comes from Greek κατακλυσμός (kataklusmos), "deluge", from κλύζω (kluzo), "wash away, flood", and κατά- (kata-), "down". It refers to the flooding of all Earth, usually by endless rains and rising rivers, as it is told in the story of Noah's Ark in the book of Genesis in the Old Testament. Note that this myth also exists in many other Oriental cultures. In many cultures, possibly including Judaism, this is a recurring event, by which time is cyclically ordered in periods of growth and subsequent destruction. It now means a great, uncontrollable disaster, but not necessarily so great as to destroy civilization. It should have significant destructive impact within a certain environment. There is some overlap with apocalypse.
Armageddon (Ἁρμαγεδών in Greek) is the hill in Israel where the final battle between the Christian Messiah and Satan is to take place at the end of time, the Last Judgement. The word appears only once in the Bible, so says Wikipedia, in the book of Revelation. Similar stories about a battle on a mountain at the end of time already existed in Jewish lore before Christ, and were also adopted by Islamic prophecies. Armageddon is used as a near-synonym of apocalypse in modern English; I don't see any difference except that it has a slight connotation of violence and struggle, whereas apocalypse is slightly more abstract, "cleaner". In most contexts there is no difference.
Modest describes the personality trait or behaviour of not flaunting oneself, talking oneself up or putting oneself on display.
Modest behaviour can be a response to compliments, praise or follow an achievement. Modesty can also manifested physically (for example, "dressing modestly", "modest accessories", "modest smile").
In contrast, "humble" refers specifically to a person's inner state and feelings. A humble person is willing to accept or respect another's authority, intellect and wisdom, or superiority without trying to challenge it or trying to assert oneself.
In summary, being modest refers to your behaviour, being humble refers to your ego.
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Both other comments are quite literal about traveling, but here are two metaphors, too:
On the way is when you're actively progressing. You've got a goal in mind and are traveling towards it.
On the road doesn't really mean progress, but discovery. As an analogy "on the road" implies meandering, getting around, and experiencing things. It's a relatively long duration with no particular goal.