-ennial
occuring periodically, in years:
occuring periodically, in years:
biennial, triennial, bicentennial
-en·nial
\|enēəl, |enyəl\  adjective combining form 
Etymology: Middle English -eniale, from Middle French -ennial, from Latin -ennium (as in biennium period of two years) + Middle French -al — more at biennial 
 : recurring at or marking intervals of (so many) years 
< biennial >
< centennial >
< biennial >
< centennial >