A Homonym is a word that is written and pronounced the same way as another, but which has a different meaning.
AN EXAMPLE OF A HOMONYM:
'Lie' can be a verb meaning to tell something that is not true or to be in a horizontal position. They look and sound the same, but are different verbs as can be seen from their forms:
Lie-lied-lied (to say something untrue)
Lie-lay-lain (to be in a horizontal position)