Neginoth, or Neginah - Instrumental music; by implication, a stringed instrument; by extension, a poem set to music; specifically, an epigram.
Nehiloth - A flute. From Matthew Henry's Commentary: "It is conjectured (and it is but a conjecture) that is signifies wind-instruments, with which this psalm was sung, as Neginoth was supposed to signify the stringed-instruments."
Nethinim - Servants of the priests and Levites in the menial services about the tabernacle and temple.
Niter - Mineral potash (so called from effervescing with acid). Other Bible translations use the word, lye, instead of niter.
Obeisance - A bow or courtesy; an act of reverence made by an inclination of the body or the knee. Genesis 37.
Oblation - Anything offered or presented in worship or sacred service; an offering; a sacrifice.
Obstinate - 1) Stubborn; pertinaciously adhering to an opinion or purpose; fixed firmly in resolution; not yielding to reason, arguments or other means. 2) Not yielding or not easily subdued or removed; as an obstinate fever; obstinate obstructions; an obstinate cough.
Omer - A Hebrew measure, the tenth of an ephah. See Exodus 16:36.
Oracle - 1) Among Christians, oracles, in the plural, denotes the communications, revelations or messages delivered by God to prophets. In this sense it is rarely used in the singular; but we say, the oracles of God, divine oracles, meaning the Scriptures. 2) The sanctuary or most holy place in the temple, in which was deposited the ark of the covenant. 1st Kings 6.
Over against - Across from; in contrast with; opposite.