The Pali word that Buddhists use is nibbana . . . but it is difficult using words to explain something like enlightenment because nibbana, or enlightenment, is not actually a thing it is an experience.

For example: what words would you use to explain the taste of an orange? Sweet? Sticky? Juicy? The words aren't the same as the taste though, are they? You have to taste it to really know. What words might you find in Buddhist books to describe enlightenment? How about Freedom? Peace?Love? Liberty?

How could you draw a picture of these?

In the example of the orange you could maybe draw an orange with juice dripping out onto a tongue. But what could you draw to show freedom? peace? love? or enlightenment?

When Buddhists think about enlightenment they think about the historical Buddha, Siddhattha Gotama.

So when, many many years ago, Buddhists thought about making a symbol to represent enlightenment, they thought about Gotama and made statues that looked like a human being.