The word koshirae is derived from the verb koshiraeru (拵える?), which is no longer used in current speech. More commonly "tsukuru" is used in its place with both words meaning to "make, create, manufacture." A more accurate word is tōsō (刀装?), meaning sword-furniture, where tōsōgu (刀装具?) are the parts of the mounting in general, and "kanagu" stands for those made of metal. Gaisō (外装?) are the "outer" mountings, as opposed to tōshin (刀身?), the "body" of the sword.
A koshirae should be presented with the tsuka (hilt) to the left, particularly in times of peace with the reason being that you cannot unsheathe the sword easily this way. During the Edo period, many formalized rules were put into place: in times of war the tsuka should be presented to the right allowing the sword to be readily unsheathed.
Koshirae were meant not only for functional but also for aesthetic purposes, often using a family mon (crest) for identification.
Read more about this topic: Japanese Sword Mountings