Noun of the word 'simple' is ______.

Simple এর noun form হচ্ছে Simplicity. 
Simplicity [সিম্‌প্‌লিসাটি]  (noun)  [uncountable noun]: 
• English Meaning: the state of being simple, uncomplicated, or uncompounded. 
• Bengali Meaning: সহজতা; সারল্য। 
Example sentence: He spoke with admirable simplicity.

Source: Merriam-Webster Dictionary, Accessible Dictionary by Bangla Academy.