Latin septem, seven.
A septet is a group of seven people playing music or singing together; septuplets are seven children born at one birth. A septcentenary is the seven-hundredth anniversary of a significant event; septennial can refer to some event recurring every seven years, or to a period of seven years; as a noun septenary is a group or set of seven, but as an adjective it refers to something divided into seven. September was originally the seventh month of the Roman calendar. For septillion see the entry Number words.
Related words are formed from Latin septuaginta, seventy: septuagenarian, a person in his or her seventies; Septuagesima (literally ‘seventieth day’), the third Sunday before Lent and the seventieth day before Easter Sunday; the Septuagint is the Greek Old Testament, traditionally attributed to 72 translators working under divine inspiration.
See also hepta‑.
Words such as septicaemia and septic come instead from the Greek sēptikos, rotten or decayed.