The Collaborative International Dictionary
Septi-
Septi- \Sep"ti-\, [L. septem seven.] A combining form meaning seven; as, septifolious, seven-leaved; septi-lateral, seven-sided.
Douglas Harper's Etymology Dictionary
septi-
before vowels sept-, word-forming element meaning "seven," from Latin septem (see seven).
Wiktionary
septi-
pre. seven