I have only seen this word in the book "Differential and Integral Calculus" by Augustus De Morgan and in letters relating to this book. e.g.
On page 108 of the above book, (lines 8, 9, 10 from the top) : "By [the integral of] UdV we mean ... p. 102. where the values of ΔV in the several terms are different. but comminuent."
Thus I might suggest it is a mathematical word, yet I cannot immediately make sense of it as an adjective derived from the Latin comminuō.
Thank you for your help.
Edit: The book was wrongly named as 'Elementary Illustrations of the differential and integral calculus' - thanks go to @MetaEd for the correction