Cocktail attire vs. semi-formal?

I'm finalizing my invitation wording and would love some feedback. I've done a lot of research online but have yet to find a definitive answer.

I'm having an afternoon wedding (ceremony 12:30-1p, cocktail hour 1-2p, reception 2-6p).

I want the guests to dress on the formal side (but definitely not black tie). Which wording do you think is better: cocktail attire or semi-formal?

Also, would you know what to wear if you saw either one on an invitation?

I know I can't control what anyone wears, I just don't want the time of day to be misleading.