octagonal       
adjective uk/ɒkˈtæɡ.ən.əl/ us/ɑːkˈtæɡ.ən.əl/
 八角形的
having eight straight sides
  an octagonal tower 八角塔 
 There were pictures on every other wall of the octagonal shaped room. 八角形房间的每隔一面墙上都有照片。 
 See: octagon
 - More examples
 - There will be a garden of palm trees in the central octagonal gallery.
 - Four rows of octagonal pillars support the roof.
 - An octagonal pavilion lies at the far end.