Assalam-u-Alaikum Dear Aspirants!
This very post of mine is related to the preparation of #Synonyms and #Antonyms.
There are different schools of thought when it comes to the preparation of Synonyms/Antonyms.
One school of thought opines that an aspirant had better cram the vocabulary from the GRE words. Whereas, the other one is of the view that the aspirants should practice and memorize the words from the past papers.
Well, my approach towards the preparation of this very portion is relatively different.
I would suggest tackling this very part from the linguistic point of view.
Let us study the nature of this very part and try to unfold the techniques.
First of all, you need to understand few terms.

#Morphology: “It is the study of the internal structure of words, and the rules by which words are formed.”

#Word: “The smallest of linguistic unit which can occur on its own in speech or writing.”

#Morpheme: “A morpheme is the minimal meaningful unit of a language.
e.g. un+system+atic+cal+ly

Examples of Morpheme:
1. One MorphemeBoy, Desire, Water
2. Two Morpheme Boy+ish
3. Three Morpheme Boy+ish+ness
4. Four Morpheme Gentle+man+li+ness

#Types_of_Morphemes
There are many types of morpheme but we are going to discuss the relevant ones.
1. Bound Morphemes: These are the ones that are dependent and have to be attached to the word. These are also known as Affixes (Prefixes and Suffixes)
e.g. ness, ly, ist, est, ish, ess, es, ies, etc.
2. Free Morphemes: These are the ones that are independent and do not necessarily have to be attached to the word. These morphemes can stand alone as words.
e.g. girl, system, hope, etc.
3. Derivational Morphemes: These are actually bound morphemes when combined with a free morpheme, change either the semantic meaning or part of speech of the affected word.
e.g. Adjective + Derivational Morpheme = Adverb  Quick+ly = Quickly

I am quite positive that the aforementioned terminologies must be clear to you now.
Let us come to the point as to how this all can help you in solving Synonyms/Antonyms portion.
You do come across very strange words that are quite alien to you. These are the words that are quite novice to you of which you have never heard or read anywhere.
The morphemes can actually help you guess the word more accurately rather than going for a totally blind fluke.
For instance, the morpheme "vid/vis" generally refers to "view". If you know this thing then you can easily understand meanings of the words you have never heard of or read before.
e.g. video. vision, visual. evidence. and many more such words which will give you the sense of the word.
The word “insomnia” actually consists of three parts, (in+somn+ia) where ’in’ means without, ‘somn’ means sleep, and ‘ia’ means state. Therefore, one can easily infer that ‘insomnia’ actually refers to a state in which a person is without or unable to sleep.
If you ever come across the morpheme ‘somn’ then you must be alert that it actually stands for ‘sleep’. This very ability will help you have a very educated guess even if you do not understand the given word completely.
The words such as spectacle, spectrum, prospect, aspect, spectacular, inspection, inspector, etc, have something in common and that is "spec". So, one can easily develop the sense that all these words have more or less the similar meanings because of having a common morpheme (spec) among them.
This is how Morphology can help you out in Synonyms/Antonyms.
Furthermore, the Derivational Morphemes can help you understand as to which part of speech the word belongs to.
e.g. Choose the word synonymous to the word “cristonatious”
a. Fight
b. Quickly
c. Create
d. Beautiful

The options are quite simple but you must have never heard of the word “cristonatious”. But you can easily judge that ‘ious’ is actually a Derivational Morpheme that is used for the words that are adjectives. Therefore, the correct option has to be ‘Beautiful’ because it is the only adjective among the given options.

Note: Alongside this very technique, you had better cram the GRE words along with words from DAWN newspaper.
I am also sharing the list of Bound Morphemes along with their meanings and examples.
Best of luck.

Regards,