What is the past tense of word legible?

The word "legible" is an adjective, meaning "readable." Adjectives don't have tenses like verbs do.

If you are looking for a word to describe something that was readable in the past, you could use:

* Was legible

* Could be read

* Was decipherable

For example:

* "The ancient inscription was legible."

* "The faded letter could be read."

* "The scribbled notes were decipherable."