Wikipedia makes much use of descriptive words to describe different groups of populations and languages that I find quite fascinating to learn:
Demonym: from the Greek 'demos', populace, often used by geographers, denoting the members of a people or the inhabitants of a place.
Someone called a Briton has genetic ancestors from Britain, while anyone holding a British passport is considered British.
The Franks settled France, but its' citizens are French.
Ethnonym: from the Greek 'ethnos', name, is the name given to a given ethnic group, and can be divided into exonyms where the name of the ethnic group has been created by another group of people [ say, Germans ] and autonyms where the name is created and used by the ethnic group itself [ say, Deutsch ].
Ethnonyms can become political, and evolve from acceptable to unacceptable [ say, Gypsy
has referred to the Roma ]. Other examples include Vandal, Bushman, Barbarian and Philistine.
Euphemism: from the Greek for 'good/well' and 'speech/speaking', is the substitution of a less offensive expression in place of one that may offend or suggest something unpleasant to the listener; or in the case of doublespeak, to make it less troublesome for the speaker. Someone who died, 'passed away' .
Comedians make jokes of euphemisms and intend for them to be funny. Also used in job titles,
for example, a 'transparent-wall maintenance officer' is a 'window cleaner'.
The Euphemism Treadmill: In a well-known linguistic process known as pejoration, recently dubbed the "euphemism treadmill" by Steven Pinker, euphemisms often evolve into taboo words. [ 'toilet room', replaced by U.S. 'bathroom' and U.K. 'water closet' became U.S. 'restroom' and U.K. 'W.C.' ].
Adults used to be 'mentally retarded' but are now 'mentally challenged'.
Wikipedia says that a similar progression occurred with:
lame → crippled → handicapped → disabled → physically challenged → differently abled
( 'Lame', having faded in use, reportedly has been revitalised as a slang word meaning 'not living up to expectations').
Also, 'shell shock' and 'PTSD' are the same concept:
Shell shock (World War I) → battle fatigue (World War II)→ Operational exhaustion (Korean War) → Post-traumatic stress disorder (Vietnam War)
Certain euphemisms are controversial. 'Visually impaired' could mean any one of 'blind', 'having partial eyesight' and 'having uncorrected poor vision'.
Other euphemisms are innuendo if they are understood by two people, but not a third listening.
Others common in certain circles (such as the medical field, where 'myocardial infarction' means 'heart attack') are a type of jargon.
Not always euphemisms, but profane words and expressions in English tend to be taken from three areas: religion, excretion and sex.
In many languages, words that mean "swear word" are used as exclamations instead of the actual swear word [ say, sacre in French ].
Three antonyms (opposites) of euphemisms are dysphemism [ 'snail mail' for post office mail rather than email], cacophemism, which uses vulgarities [ 'sucks' is now a milder epithet] and power words, used in arguments to make a point seem more correct, uses presuppositions, and appeals to emotions rather than logic (asking a teenager, why did you stay out that late?)
Wikipedia has many more fine examples, no doubt added by readers. It is quite an interesting exercise to learn who lives where. Where does a Leopolitan come from? (answer: Lviv, Poland).