ʼa-(unspecified person object prefix) + -Ø-(3rd person subject prefix) + -s-(stative perfective marker) + -d-(classifier) + zoh(perfective verb stem), from -zóóh(“make a mark, draw a line”)
The noun sense is a direct nominalization of the verb, and likely derives from the way that inches would be marked out, either on a ruler or on the item being measured.