I have only seen this word in the book “Elementary Illustrations of the differential and integral calculus” by Augustus De Morgan and in letters relating to this book. e.g.
On page 108 of Elementary Illustrations, (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.