On the linguistic and functional side I tend to think of an outcast term in three axes: denotation (
what happened), connotation (how the culture judges it), and morphology (does the word lend itself to compounds and titles?). Words like 'exile' and 'banished' emphasize action and distance; 'pariah' and 'outcast' emphasize social standing; 'leper' or 'untouchable' emphasize contagion and purity. Morphologically productive roots—think '-born', '-marked', '-kin'—let you build institutions and epithets cheaply: 'mark-bearers', 'pariah-wards', 'shadowborn'.
If I’m designing a culture, I choose a root that reflects
the power structure. A theocracy will have ritual terms: 'unblessed', 'apostate', 'unclean'; a mercantile republic might use legalistic terms: 'declared forfeit', 'forfeited', '
outlawed'. Phonetics matter too—harsh consonants ('pariah' has a spitting cadence) feel accusatory, while softer sounds ('castaway') feel melancholic. I also like hybrid inventions—'riftborn', 'wastemarked', 'riftlése'—to hint at magic or taboo without borrowing real-world slurs. Personally I lean toward a terse, evocative coinage that can spawn derivatives; it makes maps, edicts, and curses feel lived-in, and I get a little thrill inventing the swear-terms peasants mutter.