Decennial rhymes with:
bicentennial, biennial, centennial, millennial, perennial, quadrennial, triennial, bicentennial, biennial, centennial, ceremonial, colonial, company'll, intracranial, lineal, matrilineal, matrimonial, menial, millennial, patrilineal, perennial, quadrennial, testimonial, triennial
Decennial sounds like:
decamillo, decimal, diagonal, diagonally, dicamillo, dismal, dismally