A synonym is a word or phrase that means exactly or nearly the same as another word or phrase in the same language.
Example:
The word "brave" has many synonyms:
 
Brave.JPG
Why do we need synonyms? Synonyms are also called as similar words. They are used to avoid repetition of the same words in a text. The meaning has to be exact or very close to the exact phrase. If it can be used as a replaceable word, it is called a synonym. Sometimes if the word does not come to mind, one can always look up for synonyms, to find the exact word.
Example:
Instead of using the word "beautiful" in a text repetitively, one can use words like good looking, attractive, pretty, lovely, gorgeous etc. It makes the text more interesting to read and also provides an opportunity to express different nuances.
How are synonyms different from meanings?
Meanings tend to describe the word. Synonyms are other names for the same word, that can be used interchangeably.
In the same example as above, "meaning" of beautiful is pleasing the senses or mind aesthetically. "Synonyms" of beautiful are attractive, pretty, lovely etc.
Can synonyms be used interchangeably in all circumstances? No. One has to apply the meaning in the context and then interchange the synonym; otherwise, the sentence becomes illogical.
Example:
The synonyms of the word "next" are following, nearest, close, proximate etc.
However, each word has a unique "meaning" attached to it. Unless the meaning of the synonym matches the word, it cannot be replaced.
 
My aunt lives next door - the meaning is my aunt lives nearby, close to me.
But it cannot be replaced as,
My aunt lives following door (or)
My aunt lives the nearest door etc.
 
The "meaning" of next is "coming immediately after"
The "meaning" of following is "as a result of"
Important!
We have to be cautious while replacing synonyms for words. By choosing one synonym for the other, it can subtly (not literally), influence or change the intent and tone of the text.
For an extensive list of synonyms, click here.
Synonyms of words from the lesson "The Book That Saved The Earth":
S.No
Word
Synonyms
1
AncientOld
2
StrangeUnusual
3
DecorateEmbellish 
4
Robe Dress
5
Apprentice Junior
6
Elaborate Detailed
7
PeevishlyIrritable
8
SalutationGreeting
9
Mighty Potent
10
Ridiculous Funny
11
Insignificant Unimportant
12
Primitive Ancient
13
Pause Break
14
InvadeConquer
15
Enormous Huge
16
RiffleSkim
17
CrudeRaw
18
Staple Main/Chief
19
Strange Unusual
20
Certainly Unquestionably
21
EarthlingEarth dweller
22
FillingStuffing
23
GulpSwallow
24
DeliciousTasty
25
Surveyor Evaluator/Analyser
26
PuzzleConfuse
27
Suggest Propose
28
Intently Attentively
29
Listen Hear/Pay attention
30
TwirlSpin
31
Recall Remember
32
AppearSeem
33
Sort Kind
34
Alongside Together with
35
Unfold Open out
36
DecipherMake out/Perceive
37
SwallowConsume
38
Magnificent Excellent
39
PopTo push
40
SimultaneouslyConcurrently
41
InstantImmediate
42
Pretty Attractive/Good-looking
43
MaidFemale servant
44
ContraryOpposite
45
Rare Infrequent
46
GravelySeriously
47
AlarmingWorrying
48
HumourComedy
49
ResumeRestart
50
MomentMinute
51
InvadeConquer
52
TranscribeTranslate
53
SavedProtected
54
EstablishSet up
 
Important!
To practise more synonyms, click here.