Definition of "ironic"

It was ironic I forgot my textbook on human memory.

2014, Steven Pinker, The Sense of Style: The Thinking Person's Guide to Writing in the 21st Century!, page 275

Chloe had once seen a real-life goth hanging around by a garbage bin in the high street and become incredibly excited. She really wanted to go over and ask her how to get started in the goth world, but she was too shy. Which was ironic, since shyness is something you need if you want to be a successful goth.

2009, David Walliams, Mr Stink