measureless

From measure +‎ -less.

measureless (not comparable)

1. Not measured because it is so large that it is difficult or impossible to do so.

   Synonyms: boundless, limitless, vast

   • 1797, S[amuel] T[aylor] Coleridge, “Kubla Khan: Or A Vision in a Dream”, in Christabel: Kubla Khan, a Vision: The Pains of Sleep, London: […] John Murray, […], by William Bulmer and Co. […], published 1816, →OCLC, page 55:

     In Xanadu did Kubla Khan / A stately pleasure-dome decree: / Where Alph, the sacred river, ran / Through caverns measureless to man / Down to a sunless sea.