hexadeca-

Etymology tree
Proto-Indo-European *swéḱs
Proto-Hellenic *hwéks
Ancient Greek ἕξ (héx)
Ancient Greek ἑξα- (hexa-)der.
Latin hexa-der.
English hexa-
Proto-Indo-European *déḱm̥
Proto-Hellenic *dékə
Ancient Greek δέκᾰ (dékă)
Ancient Greek -ᾰ́ς (-ắs)
Ancient Greek δεκάς (dekás)der.
Late Latin decasder.
French déca-bor.
English deca-
English hexadeca-
From hexa- (“six”) + deca- (“ten”). Compare Ancient Greek ἑκκαίδεκα (hekkaídeka, “sixteen”).