Synonyms in English

Greek morphemes: syn (συν) – plus and onoma (όνομα) –

name
Means a word of similar or identical meaning to one or more words in the same language.
All languages contain synonyms but in English they exist in superabundance.

linguistic elements;
However, words with identical semantic elements preserve their differences

in connotations and stylistic characteristics (to be described below).

on the basis of the notional criterion.
According to it

synonyms are words of the same category of parts of speech conveying the same notion, but differing either in shades of meaning or in stylistic characteristics (V.V. Vinogradov).

the semantic criterion runs as follows:
Lexical synonyms are different words

of the same part of speech which have some common denotational component(s) in their semantic structure, but differ either in some other denotational component(s) or in some connotational component(s) and thus usually have different lexical collocability (E.B. Cherkasskaya).

criterion of interchangeability is also applied.
According to it, synonyms

are defined as words which are interchangeable at least in some contexts without any considerable alteration in the denotational meaning.
The application of this criterion is however limited.

defined in terms of linguistics as two or more words

of the same language,
belonging to the same part of speech and possessing one or more identical or nearly identical denotational meanings,
interchangeable, at least, in some contexts,
differing in morphemic composition, phonemic shape, connotations, affective value, style, valence and idiomatic use.

mind which is likely to happen.
Evaluative connotation: expectation may

be either of good or of evil, anticipation, as a rule, is a pleasurable expectation of something good, hope is not only a belief but a desire that some event would happen.
Stylistic difference: the Romance words anticipation and expectation are formal literary words used only by educated speakers, whereas the native monosyllabic hope is stylistically neutral.
Idiomatic usage: only hope is possible in such set expressions as: to hope against hope, to lose hope, to pin one’s hopes on smth, etc. Thus, neither expectation nor anticipation could be substituted into the following quotation from T. S. Eliot: You do not know what hope is until you have lost it.

from other languages: city /French/ - town /native/; chair /French/

- stool /native/, etc.
Due to abbreviation (in most cases the abbreviated form belongs to the colloquial style, and the full form to the neutral style): examination – exam, laboratory – lab, etc.
Due to the appearance of euphemisms (words used to substitute in speech some unpleasant or offensive words): «the late» instead of «the dead», «to perspire» instead of «to sweat», etc.

and co-usage of words belonging to different dialects and language

varieties:
Boat (English) – coracle (Welsh)
Girl (English) – colleen (Irish)
Lift (BrEng) – elevator (AmEng)
Autumn (BrEng) – fall (AmEng), etc.

of phrasal verbs, e.g. «to give up» - «to abandon»,

«to cut down» - «to diminish».
There are phraseological synonyms which are expressed by phrases similar semantically but different from the point of their pragmatics:
We say «to be late (for a lecture)» but «to miss (the train)».

synonymic sets.
Each synonymic set has a word which expresses

the most general idea and holds a commanding position over other words, it is called the synonymic dominant:
See, view, behold, perceive, etc.
Main, chief, crucial, critical, essential, etc.

function of substitution;
the function of precision of meaning;
the

expressive or stylistic function.

meaning, connotations, emotive and stylistic charge);
They can replace each other

in any given context without the slightest alteration in the denotational or emotional meaning and connotations;
They are a rare occasion and are found mostly in terminology or among special words: noun and substantive, functional affix, flection and inflection).

in their referential content:
to ascent – to mount – to

climb
to happen – to occur – to befall – to chance
look – appearance – complexion – countenance, etc.

expressive and evaluative overtones without explicitly displaying semantic difference:
child (neutral)

– infant (elevated) – kid (colloquial)
die (neutral) – pass away (elevated) – kick the bucket (colloquial)

traits & suppress other semantic traits of words; thus words

with different meaning can become synonyms in a certain context: tasteless – dull, active – curious, curious – responsive, etc.
Referential Synonyms
a vague term, which concerns co-referential expressions, when one denotatum can be defined differently from different points of view and in different aspects: e.g. names Walter Scott and the author of 'Ivanhoe' are co-referential because they refer to one and the same denotatum – Sir Walter Scott;

situations when writers or speakers bring together several words with

one & the same meaning to add more conviction or to make the description more vivid:
Safe & sound
Lord & master
First & foremost
Safe & secure
Stress & strain
By force & violence 
It is deeply rooted in the history of English language since it was customary to use French borrowings together with their native synonyms, especially those which are characterized by alliteration and rhymes.

in meaning.
Not every word of a language may have

an antonym though practically every word may have a synonym.
As is with synonyms, different lexical-semantic variants of a word have different antonyms:
Light – dark, light – heavy;
Bright – dim, bright – unintelligent, etc.

two or more words of the same part of speech

which have some common denotational components in their semantic structure, but express some contrary or contradictory (contrasting) notions;
They are characterized by different types of semantic contrast of the denotational meaning and interchangeability at least in some contexts.

antonyms are divided into
contradictories (intelligent – stupid, peaceful –

stormy, etc.) and
contraries (up – down, give – take, etc.).
According to their morphological structure antonyms may be subdivided into
root antonyms (intelligent - stupid) and
derivational antonyms (intelligent - unintelligent).