In Hindi, many words that end with आ are masculine, such as कमरा, लड़का, जूता, केला, बेटा.
However, not every word that ends with आ is masculine, such as चर्चा, which is feminine.
A common suffix in Hindi is –ता. This suffix comes from Sanskrit, and so it usually applies to Sanskrit loanwords. This suffix is usually preceded with अ.
An example of this suffix on a word is सुन्दरता (“beauty”).
This suffix basically abstracts a word. In other words, it converts an adjective to a noun (e.g., “beautiful” to “beauty”), or a concrete noun to an abstract noun (e.g., “friend” to “friendship”), etc.
Generally, words that have the suffix –ता are feminine.
Note that not every word that ends in –ता has the suffix –ता. For instance, the word तोता (“parrot”) is masculine, but removing the –ता produces तो, which is not a related noun or adjective (although incidentally it is a word). However, सुन्दरता (“beauty”) does have the suffix –ता because सुन्दर (“beautiful”) is a related adjective.
Consider the following examples. All of the following words are feminine.
सफलता (सफल “successful”+ ता = सफलता “success”)
सहायता (सहाय “assisting” + ता = सहायता “assistance”)
क्षमता (क्षम “capable” + ता = क्षमता “capability”)
सदस्यता (सदस्य “member”+ ता = सदस्यता “membership”)
राष्ट्रीयता (राष्ट्रीय “national” + ता = राष्ट्रीयता “nationality”)
योग्यता (योग्य “qualified”+ ता = योग्यता “qualification”)
सुन्दरता (सुन्दर “beautiful” + ता = सुन्दरता “beauty”)
आवश्यकता (आवश्यक “necessary” + ता = आवश्यकता “necessity”)
मित्रता (मित्र “friend”+ ता = मित्रता “friendship”)
एकता (एक “one” + ता = “oneness” / “unity”)