Thread:EmperorSigma/@comment-1493741-20150120173512

Its less the word itself, though it contributes, and more that the description itself lends itself correctly to that word. His energy is off the charts, it can "corrupt" people and paralyze them, with no sight of a limit on who this can effect.
 * (Spiritual Power) is an energy generated by the soul of every being, Humans, Hollows, Shinigami, Quincy, your dog, that cat, and the toilet in the neighbour's house, all generate it (As they all have souls). It is the Bleach equivalent of Chakra in Naruto, or Ki in Dragon Ball. The Bleach Wiki grades differing levels of Reiryoku in a set of tiers (Basic - High - Great - Immense) which has been adopted on this wiki as well for sake of ease (And then convoluted, because Fanon does that, with extra tiers (Tremendous, Monstrous, Unfathomable and so on). Having Unrivaled Spiritual Power would essentially be saying you're God, even if its untrue, its a pretty hefty implication.
 * (Spiritual Pressure) is an application of Reiryoku, it is the user exerting their energy as a physical pressure on the environment around them. The typical form, aptly enough, is an invisible pressure. But it can have a myriad of effects that are unique to each individual, Yamamoto's can become flame and be wielded by him, Toushiro Hitsugaya can freeze his surroundings, and did so unconsciously before becoming a Shinigami. Kenpachi Zaraki even uses his as armour. Reiatsu is almost always a comparative thing, its effects only really work on someone weaker than the individual. 