Answer:

unknown

Answer	Crossword Clue
UNKNOWN	Like X
UNKNOWN	Obscure
UNKNOWN	X, in algebra

UNKNOWN	Anonymous
UNKNOWN	x, at times
UNKNOWN	Something to solve for, in algebra
UNKNOWN	Far from famous
UNKNOWN	Inconnu.
UNKNOWN	Incalculable.
UNKNOWN	Arlington soldier
UNKNOWN	X, in math

UNKNOWN	Like the planet Pluto before 1930
UNKNOWN	Hardly a celebrity