Anniversaire qui n'est pas bon?

Today I had an interesting experience relating to language/culture gap.

I was talking to a friend, we were talking in English. As he asked me if I have any plan on Sunday, I was sort of perplexed. Not because I did not have a specific plan to tell. But because I couldn't come up with the exact words in English to explain what it was about.

My plan on Sunday would be to gather with relatives and to have a small ceremony because it has been 7 years since my grandfather (on mother's side) passed away. In Japan we usually have this ceremony/ reunion thing when it's 1st, 3rd and 7th year since someone's death.

Having reflected for a moment, I finally picked up the word which I had thought of in the first instance but had thought was not suitable in this context.

"It's the 7th anniversary."
Feeling awkward, I went on, "since my grandfather's death."

"Do you have any other words to explain it?" Said I, in no time, out of impatience.
"Hmm... No." said he, "We don't have such events."
(He was born in America, brought up there.)

Of course, the (seemingly) latin prefix of the word anniversary originally meant "year", so its connotation should be something like "annual event". However, to consider the direct origin of the word, assuming that it came from Latin through French language, made it seem even worse fitted.

For as far as I remember, the french word "anniversaire" means "birthday".
Hereon, this endeavour of earnestly trying to figure out how to express the idea that the language you are to use does not bear resulted in using the word with the opposite connotation to the original concept.

How ironic it was!
Anniversaire qui n'est pas joyeux!!
I felt like I was copletely taken over by this awkward, uneasy feeling...
Nanka kimochi waru katta kedo omoshiro katta zekk!! ( *｀ω´)