悪魔の実
Devil Fruit
Mysterious "treasures of the sea" that grant supernatural powers at the cost of ever swimming again; where they come from is one of the series' longest-guarded mysteries.
ゴムゴムの実
Gomu Gomu no Mi
The rubber Devil Fruit Luffy ate as a child — VIZ's "Gum-Gum Fruit," whose English name famously wobbled through fruit, Devil Fruit and an invented "Gum-Gum Tree" in the early volumes.
偉大なる航路
Grand Line
The sea route where the One Piece waits — "we're headed for the Grand Line!" (Luffy, Vol. 1, p.172).
覇気
Haki
Latent will-energy introduced much later in the series, projected as armor, observation, or pure conqueror's intent.
一味
Ichimi
The crew as the world names it — 麦わらの一味, "the Straw Hat band." 一味 ("one flavor" → a band bound by one aim, faintly outlaw) is the informal counterpart to the formal 海賊団 and the personal bond of 仲間; Luffy is the rare captain whose crew never takes the formal 〜海賊団 title.
ひとつなぎの大秘宝
One Piece
The legendary hoard left by the executed Pirate King at the end of the Grand Line; its in-world name literally means "the great treasure that is all one connected piece" — the same pun the English title keeps sealed.