عَصًا = a staff; عَصَايَ = my staff.
رَحًى = a millstone; رَحَايَ = my millstone.
These are maqṣūr nouns. They retain the final alif when followed by the possessive yāʾ, instead of using the sound-noun kasrah pattern.
In ʿaṣāya, the noun is mudāf and -ya is the attached mudāf ilayh.
Opening interactive controls...
Iḍāfah to Yāʾ al-Mutakallim and the Six Nouns
عَصًا = a staff; عَصَايَ = my staff.
رَحًى = a millstone; رَحَايَ = my millstone.
These are maqṣūr nouns. They retain the final alif when followed by the possessive yāʾ, instead of using the sound-noun kasrah pattern.
In ʿaṣāya, the noun is mudāf and -ya is the attached mudāf ilayh.