pres·tis·si·mo 
(prĕ-stĭsə-mō′) Music
(prĕ-stĭsə-mō′) Music adv. & adj.
In as fast a tempo as possible. Used chiefly as a direction.
n. pl. pres·tis·si·mos
A prestissimo passage or movement.
[Italian, superlative of presto, presto; see PRESTO.]