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1.
A titular role is a role in which the character says the title of the movie or play or book.
In the movie Out of Africa, when Robert Redford is teaching Meryl Streep how to drive, and there is all this traffic and this man drives up beside them and says, "Aww boy, Im just so tired of all this traffic, I can't wait until I get out of Africa.

Or

In the movie Starwars, when that Raiders of the Lost Ark guy is teaching Luke how to drive. He's teaching Luke how to drive the thing, and they are in the back messing with the feathers, and this stowe-away walks by and says, "Aww boy, Im just so tired of all these star wars."

The man who says these lines has the title line, and the titular line.
by PatientJobe November 05, 2006
 
2.
Adjective form of "title."
A young Keanu Reeves made his stage debut starring as Oliver!'s titular character.

The above is no fact. It is merely written out for example's sake.
by Henry Gibson October 27, 2005
 
3.
A predominately male expression derived from their fascination with breasts. Use as a slang term to describe something which is 'cool'.
"Dude! That's just titular!"
"Titular, just titular! It couldn't BE more titular!"
by Wod February 08, 2003