Homonymy, Homophones and Homograph

A HOMOGRAPH

A homograph is a word that has the same spelling as another word but has a different sound and a different meaning:

lead (to go in front of)/lead (a metal)

wind (to follow a course that is not straight)/wind (a gust of air)

bass (low, deep sound)/bass (a type of fish)

A HOMOPHONE

A homophone is a word that has the same sound as another word but is spelled differently and has a different meaning:

to/two/too

there/their/they're

pray/prey

The ending –graph means drawn or written, so a homograph has the same spelling. The –phone ending means sound or voice, so a homophone has the same pronunciation. But here's where it gets tricky. 

(https://www.vocabulary.com/articles/chooseyourwords/homonym-homophone-homograph/)

HOMONYM 

The –onym root means “name.” You also hear it in anonymous, which literally means “without a name,” and of course, in the words synonym and antonym. Homonyms are words that have the same name; in other words, they sound the same and they’re spelled the same. For example, pen meaning the writing instrument, and pen meaning an enclosure for an animal, are homonyms. They have the same pronunciation, “pen,” and they’re both spelled P-E-N. To put it another way, homonyms are both homophones and homographs! You can even illustrate this with a cute little Venn diagram of two overlapping circles. One circle contains homophones; the other circle contains homographs; and the football in the middle contains homonyms.

So homophones sound the same; homographs are spelled the same; and homonyms do both. That’s all you need to know. 

At this point, if you already knew the difference between the three words, you might be saying, “Now hold on just one minute! Homographs are words that are spelled the same, and don’t sound the same! Homophones are words that sound the same, but aren’t spelled the same!”

This is where my fingers and thumbs analogy comes in. Sure, when somebody says, “Ow! I cut my finger!” you probably figure they cut their pointer, tall man, ring finger, or pinky. That’s because if they’d cut their thumb, they’d probably have been more specific and said, “Ow! I cut my thumb!” Even so, you agree that a thumb is a finger—a special finger, but still a finger. In the same way, it makes more sense to say that pen and pen are special homophones than to say they’re not homophones. And by the same reasoning, it’s simpler to think of pen and pen as special homographs than say they’re not homographs. 

Of course, if you really want to, you can write the definitions of homophone, homonym, and homograph so that there’s no overlap, but I suspect that definitions like that are part of the reason for people’s confusion.

(http://www.quickanddirtytips.com/education/grammar/homophones-homographs-and-homonyms)