just indicates the number of **years** that something has been in continuing or in operation. This term is used in regards to anniversaries, but only as a description of what the anniversary is for.
is remembrance or commemoration. Adding to it makes it 'Commemoration **Day** ', or 'Anniversary'.
These two terms are often used together to indicate both the celebration/commemoration and what specifically it is celebrating.
> 10 **** () ****. Day of celebration of 10 years of marriage; 10-year (marriage) anniversary.