One word Substitution is one of the integral parts of vocabulary. It is asked in various competitive exams like IBPS PO/ Clerical, SSC, LIC, CDS etc. It simply means that a sentence has to be replaced with a single word. This area requires a good vocabulary to solve the questions well.
For example: A hater of womankind - Misogynist
One easy method of doing one word substitution is by using the root method. Roots are nothing but the words from which the main word has been derived. In our other series of vocabulary we have consolidated the lists of root words that will ease your preparation.
For example: Look at the root word - CRACY.
Learning through word roots will make it easy for you to grasp more and enhance your vocabulary. The above given link of word roots will surely help you in this regards. It's always advisable to learn one word substitution with the help of word roots to ease your vocabulary building and expand your word base exponentially.