decadeslong

decades +‎ -long

decadeslong (not comparable)

1. Lasting for decades.
   • 2007 July 13, Kyle Whitmire, “Suit in U.S. Over Murders in Colombia”, in New York Times‎:

     From the start of its operations in Colombia, the company was on guard against the decadeslong civil strife in the country between left-wing guerrilla and right-wing paramilitary groups, witnesses have testified.

• multidecade

• decade-long, decadelong (only 1 decade)
• yearslong