Stylistic semasiology

Synecdoche. Synecdoche is a variety of metonymy. It consists in using the name of a part to denote the whole, or vice versa. E. g.: «То be a comrade with a wolf and owl...». In this example «wolf» and «owl» stand for wild beasts and birds in general.
Periphrasis. Periphrasis is in a way related to metonymy. It is a description of an object instead of its name. E. g.:
«Delia was studying under Rosenstock — you know his repute as a disturber of the piano kevs» (instead of «a pianist»).
It is the renaming of an object by a phrase that foregrounds some par­ticular feature of the object. The most essential feature is substituted for its name:
e.g. The Dark Continent (Africa).
The essence of this SD is that it is contextual. An easily decipherable pe­riphrasis is not a SD but a synonymous expression fixed by social practice which is called traditional language periphrasis:
e.g. an affair of honour (duel), gentlemen of the long robe (lawyers).
Periphrasis serves to achieve greater expressiveness and is often used for the sake of humor, satire, parody:
e.g. a strange specimen of human race (a cabman).
Sometimes they are used for bombastic effect, when something is elevated, hallowed:
e.g. "That punctual servant of all work-the Sun" (Ch. Dickens).
There are some types of periphrasis that require competence for being de­ciphered. Stylistic periphrases can be devided into:
e.g. logical — the author of Hamlet,
figurative — the swan of Aven
(metaphorical or metonymical).
Actually, in their essence there is no difference between metaphor and figurative periphrasis, the latter being a combination of words which stand for one concept, but this roundabout description does not suggest similarity in so direct a way as in case of metaphor and often requires explanation:
e.g. "Mr. Grandgrind then returned with promptitude to the national cinder heap and resumed his sifting for the odds and ends he wanted and his throwing of the dust about into the eyes of other people who wanted other odds and ends — in fact, resumed his parliamentary duties" (Ch Dickens).
Euphemism. It is a particular kind of periphrasis. Euphemism is a roundabout description of a thing considered too fearful or too rude to be named:
e.g. The Old Gentleman (the devil).
It is a whitewashing device: a milder or softer expression is used for one more rude or unpleasant. The desire to avoid naming a thing may be due to awe, fear, superstition, prejudice, social conventions:
e.g. unmentionables (underlinen).
The sources of euphemism may be traced to the practice of taboo, to man's ignorance and fear of nature, of evil spirit, of wild animals, to his belief in the magic of words. Euphemisms are generally devided into:

1. 
   religious: e.g. the Lord (God);
   
2. 
   moral and conventional: e.g. to perspire (sweat);
   
3. 
   political (reflecting hypocrisy):
   

e.g. a conflict (war), to stop payment (go bankrupt).
As you see primitive man's and modem man's motives to use euphemism are due to different causes. Thus the aim of political euphemism is to mislead public opinion.
Euphemisms very quickly grow stale and reqeure another to replace it:
e.g. lavatory — water closet — oo.