Late 16th century: via Latin from Greek pentagōnon, neuter (used as a noun) of pentagōnos 'five-angled'.

• The Greek expertise in geometry means that many geometrical forms have Greek names. The five-sided pentagon is formed from penta ‘five’ and gonia ‘angle’, just as polygon (late 16th century) is formed from the word for ‘many’ plus -gon and diagonal (mid 16th century) with dia ‘through’. Penta is also found in words such as the mystic figures of the pentangle (Late Middle English), pentacle (late 16th century), and pentagram (mid 19th century), and in the pentathlon (early 17th century), once the original five events of leaping, running, discus-throwing, spear-throwing, and wrestling of ancient Greek and Roman games. Fifty is found in Pentecost (Old English) which came via ecclesiastical Latin from Greek pentēkostē (hēmera) ‘fiftieth (day)’. The Jewish festival of Shavuoth is held on the fiftieth day after the second day of Passover. The Christian festival is held on the seventh Sunday after Easter commemorating the descent of the Holy Spirit on the disciples as recorded in Acts 2.