Yes, GUAIACUMS is a Scrabble word!

Letter values in Scrabble US: G 2, U 1, A 1, I 1, A 1, C 3, U 1, M 3, S 1.

Is it a valid word?

GUAIACUMS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

medicinal resin from the lignum vitae tree
hard greenish-brown wood of the lignum vitae tree and other trees of the genus Guaiacum
small genus of evergreen resinous trees or shrubs of warm and tropical America

Also: lignum vitae, genus guaiacum.