Aazusayumi is a bow made of Japanese cherry birch used for Shinto rituals. Any bow can be called an Azusayumi, regardless of the material it is made from.
Or it is a Makura word (Poetic epithet convention)
In the old days it was used as a bow (meigen - resounding bowstrings) that makes a sound for the amulet used in Shinto rituals and childbirth. The bow was presented to shrines in Kyoto from Kai and Shinano Provinces, and some examples are still in existence today (three bows in Shoso-in chuso storage).
Azusayumi does not have a fixed shape and how it is shaped depends on where it is used; the bow used in Hosha-sai Festival (an archery ceremony that drives evil away) of Fushimi Inari-taisha Shrine is simply a branch of cherry birch with a bowstring; the bow used in the transfer of a deity to a new shrine building once in a prescribed number of years was made by kyo-yumi bow maker Kanjuro SHIBATA using a technique handed down from previous generations.
Azusayumi as a Makura word
This word preceded spring (a homonym of setting up the string) and pulls in Manyoshu (Collection of Ten Thousand Leaves).