-आई

From Old Hindi -आई (-āī). As this suffix can be applied to both nominals and verbs, possibly from a merger of:

• Prakrit -𑀅𑀇𑀆 (-aïā), Sauraseni Prakrit -𑀅𑀤𑀺𑀕𑀸 (-adigā), from Middle Indo-Aryan -𑀓- (-ka-) + -𑀢𑀸- (-tā-) + -𑀇𑀓𑀸- (-ikā-), pleonastic suffixes attached to Sanskrit -ता (-tā), from Proto-Indo-European *-teh₂. This makes it a cognate through Indo-European with English -ty.
• Prakrit -𑀆𑀯𑀺𑀆 (-āviā), from Sanskrit -आपय (-āpaya, “causative-forming suffix”) + Middle Indo-Aryan -𑀇𑀓- (-ika-). See Sanskrit -आपयति (-āpayati), Hindi -आना (-ānā) for more.

• (Delhi Hindi) IPA^(key): /ɑː.iː/, [äː.iː]

-आई • (-āī)

1. Forms feminine abstract nouns.

• Bahri, Hardev (1989) “-आई”, in Siksarthi Hindi-Angrejhi Sabdakosa [Learners' Hindi-English Dictionary], Delhi: Rajpal & Sons.
• Platts, John T. (1884) “-आई”, in A dictionary of Urdu, classical Hindi, and English, London: W. H. Allen & Co.
• Jaroslav Strnad (2013) Morphology and Syntax of Old Hindī : Edition and Analysis of One Hundred Kabīr Vānī Poems From Rājasthān (Brill's Indological Library; 45), Leiden, →OCLC, page 232