septendecennial

Borrowed from Latin year from Latin septendecim (“seventeen”) [from septem (“seven”) + decem (“ten”)] + -al (suffix forming adjectives). By surface analysis, septendec- +‎ -ennial.

• IPA^(key): /ˌsɛptəndɛˈsɛn.i.əl/
• Rhymes: -ɛn.i.əl

septendecennial (not comparable)

1. (rare) Occurring every seventeen years; pertaining to or designating a seventeen-year interval.
   • 2025, Henry Feinberg, Entomological Patterns and Lexical Precision:

     The septendecennial emergence of Magicicada septendecim represents one of the most remarkable synchronized reproductive cycles in the animal kingdom, with entire broods surfacing after precisely seventeen years underground.

• heptadecennial (less common)

• tredecennial
• centennial
• biennial, triennial, decennial, millennial

• periodical cicada
• Magicicada septendecim