oc ‧ ta ‧ gon /ˈɒktəɡən $ ˈɑːktəɡɑːn/ BrE AmE noun [countable]
[ Date: 1500-1600 ; Language: Latin ; Origin: octagonum , from Greek , from okta- 'eight' + -gonon '-gon' ]
a flat shape with eight sides and eight angles
—octagonal /ɒkˈtæɡən ə l $ ɑːk-/ adjective :
an octagonal tower