Orgel, organ.

Oriktig, wrong, erroneous.

Orimlig, absurd, nonsensical.

Orimlighet, absurdity.

Orka, can, to be able.

Orkan, hurricane.

Orklös, weak, feeble, infirm.

Orlofssedel, character.

Orm, serpent, viper, adder.

Ormbunke, fern.