A portmanteau of the words, "urine" and, "silencing".
The act of, when passing micturition (urine), pissing onto the inside of the toilet bowl above the waterline or against the back wall of a wall urinal so that the, "urine splashing into water" sounds are totally absent.
{Husoos}: Hey Horhay, where's Edgar? He went into that restroom a few minutes ago, but I don't hear any pissing sounds.
{Horhay}: Edgar is urincing -- that way nobody will hear him peeing.