Yes, it means unrehearsed or unprepared
The origin of the word impromptu is french. The definition is having no preparation.
He surprised the cast by making an impromptu appearance on stage.
Your impromptu adlibs are NOT appreciated as you keep STEALING THE SCENE! The impromptu picnic was held sans ants.
The magician entertained us with an impromptu card trick.
My sentence would be: At school we had to do an impromptu speech which was pretty hard to do but it was worth all the effort!
unplanned off-the-cuff impromptu
The word impromptu begins with i and ends with u.
The word you're looking for is "impromptu."
Impromptu.
Innuendo, impromptu, anecdote, abominable, ennui
secretly impromptu wildcatting striking
Impromptu is the closest to spontaneous word. It is a word representing sudden action.