pris ‧ m /ˈprɪz ə m/ BrE AmE noun [countable]
[ Date: 1500-1600 ; Language: Late Latin ; Origin: prisma , from Greek , 'something cut with a saw' ; because of its shape ]
1 . a transparent block of glass that breaks up white light into different colours
2 . technical a solid object with matching ends and several sides which are the same width all the way up