It's not as simple as you think.
People often think that by merely adding prefixes (un, dis or im) to a word, you can change its meaning.
For example:
In (prefix) + correct (word) = incorrect
In + accurate = inaccurate
Mis + lead = mislead
But there are exceptions to this rule.
Take, for example, the word famous. You might think it's the opposite is infamous, but it's not.
Famous means 'known by many people'.
Infamous people are also well-known, but for the wrong reasons.
Just by adding 'in' to famous, you don't get its opposite word. Incidentally, the opposite of famous is obscure.
Take this Quiz to test your English language skills with 10 such words.
Quiz: Anita Aikara
Illustration: Uttam Ghosh/Rediff.com