Crossword Clue:

SIGMA a Greek letter

Answer	Crossword Clue
TAU	Greek letter shaped like a cross
OMEGA	Greek letter shaped like a horseshoe
DELTA	Airline whose name is a Greek letter

GNU	Animal whose name sounds like a Greek letter
PSI	Greek letter spelled out at the start of a Beatles title?
TAU	Letter after sigma
RHO	Letter before sigma
RHO	Letter between pi and sigma
TAU	Letter between sigma and upsilon