hep ‧ ta ‧ gon /ˈheptəɡən $ -ɡɑːn/ BrE AmE noun [countable]
[ Date: 1500-1600 ; Language: Greek ; Origin: heptagonos , from hepta 'seven' + gonia 'angle' ]
a shape with seven straight sides ⇨ polygon
—heptagonal /hepˈtæɡən ə l/ adjective
hep ‧ ta ‧ gon /ˈheptəɡən $ -ɡɑːn/ BrE AmE noun [countable]
[ Date: 1500-1600 ; Language: Greek ; Origin: heptagonos , from hepta 'seven' + gonia 'angle' ]
a shape with seven straight sides ⇨ polygon
—heptagonal /hepˈtæɡən ə l/ adjective
Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012