Every 10 seconds, Nocturne's next attack strikes surrounding enemies for 120% of his physical damage and heals himself for 15-40 (at levels 1-18) (+15% of ability power) per target hit. Nocturne's basic attacks reduce this cooldown by 1 second (2 seconds against champions).
something i've been curious about: does every basic attack reduce this cooldown by 1 second (i.e., with 5 attacks, the CD would be 5 seconds), or does it just reduce to 9 seconds as long as you attack at all?
Every basic attack reduces the cooldown by 1 second.
So after 5 attacks, the cooldown would be 5 seconds.