Titular is an adjective that means related to a title. 

The Latin word titulus (TEA too loose) means name, and was morphed into the word title in late 16th century. Our word of the day is an adjective that came around soon after. Here’s an example of titular in use:

I love the Charles Dickens novel David Copperfield, but found the titular character kind of boring. You’d think if someone’s name was used as a title of a book, they’d be more dynamic and charismatic.