1) Amazingly large or great 2) Astounding 3) Astounding, wonderful 4) Causing amazement 5) Colossal 6) Large 7) More than great 8) Prodigious Found on https://www.crosswordclues.com/clue/stupendous
Stu·pen'dous adjective [ Latin stupendus astonishing, p. future pass. of stupere to be astonished at. Confer Stupid .] Astonishing; wonderful; amazing; especially, astonishing in magnitude or elevation; as, a stupendous pile. 'A stupendous sum.' Macaulay. ... Found on http://www.encyclo.co.uk/webster/S/216