counter for soakings (of fabric in a dye)
Archaic suffix and counter used specifically for counting the number of times fabric is soaked in a dye bath. Not used in modern Japanese outside of historical or specialized dyeing contexts.
An old document says this cloth was dyed with three soakings.
still more; especially; all the more
soaking in dye many times
The reading しお is an archaic counter for dye soakings, likely derived from the verb 染む (しむ, to dye) or related dyeing terminology. The exact derivation is uncertain.