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The description of the word you requested from the astronomical dictionary is given below.
'spi‧ral 'ga‧lax‧y
A spiral galaxy is a galaxy with a flat disk in which (when seen from above) bright "arms" appear to come from the center. A spiral galaxy also contains a number of globular clusters, of which most are outside of the disk. In the center of the disk there may be a bar-shaped structure: then the galaxy is a barred spiral galaxy.