Source : WordNet®

air sock
     n 1: a truncated cloth cone mounted on a mast; used (e.g., at
          airports) to show the direction of the wind [syn: {windsock},
           {sock}, {wind sleeve}, {wind cone}, {drogue}]
     2: truncated cloth cone used to indicate wind direction [syn: {air
        sleeve}, {wind sock}, {wind sleeve}]