Yes, REFLEXION is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, F 4, L 1, E 1, X 8, I 1, O 1, N 1.

Is it a valid word?

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

the phenomenon of a propagating wave (light or sound) being thrown back from a surface
expression without words
a remark expressing careful consideration
a calm, lengthy, intent consideration
the ability to reflect beams or rays
a likeness in which left and right are reversed
the image of something as reflected by a mirror (or other reflective material)

Also: mirror image.