Definition of "assur"

Wool which has been shorn from it or which has fallen off it is assur (prohibited for any beneficial use) and if it becomes mixed with other wool the whole becomes assur (Y.D. 308).

1968, Samson Raphael Hirsch, Horeb: A Philosophy of Jewish Laws and Observances

In their commentary, the Tosafot conclude that it is assur to inflict a wound in one's body (chovel be'atzmo) even if he benefits from it.

2006, Rabbi Alfred S. Cohen, editor, Journal of Halacha and Contemporary Society, numbers 51–56

After chatzos it is assur to daven shacharis.

2011 February 23, Philogos, “How To Understand Yeshivish”, in The Forward‎