Boundlessly dire dregs, dull, dark and disorderly (9)
I believe the answer is:
irregular
'disorderly' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for irregular that I've seen before include "Erratic" , "Rough - guerrilla" , "Disorderly, uneven" , "unlike full-time soldiers" , "one of Holmes's Baker Street urchins" .)