Yes, GEODESIC is a Scrabble word!

Letter values in Scrabble US: G 2, E 1, O 1, D 2, E 1, S 1, I 1, C 3.

Is it a valid word?

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

(mathematics) the shortest line between two points on a mathematically defined surface (as a straight line on a plane or an arc of a great circle on a sphere)

Also: geodesic line.

Not playable in Scrabble US: GEODESICAL.