unputdownable

adjective2

1. •
   (informal) Of a person, etc.: difficult or impossible to put down (in various senses).

   • Finally, we appeal to all right-minded playgoers. Let them remember that they have got tongues, and that a vigorous, unmistakeable, un-put-downable hiss is, in a theatre, a potent instrument. — 1861
2. •
   (informal) Of a book or other written work: so captivating or engrossing that one cannot bear to stop reading it.

   • I found it absolutely (or almost) unputdownable and at the same time as complete a waste of time in a sense as one of [Erle Stanley] Gardner's Perry Mason stories, which I also find unputdownable. — 1947