Other forms: commemorated; commemorating; commemorates
To commemorate something means to remember something and by doing so to honor it, as in “We would like to commemorate his many years of past service by presenting him with this lovely gold watch.”
The word commemorate has a pretty clear echo of memory in it, so it can help to keep it in your mind just by noticing that. You might also notice that you’ve seen the word before, either in late-night infomercials or in various advertisements in magazines, when they talk about commemorative plates, or stamps, or coins: little things that are supposed to honor events or people by recalling them to our collective memory.