As a scientific term, "diminishing" means its derivative has limit/asymptote of 0 or negative approached fast enough that the integral (or series sum) is bounde

As a scientific term, "diminishing" means its derivative has limit/asymptote of 0 or negative approached fast enough that the integral (or series sum) is bounded. Logarithm, with derivative 1/x is the well-behaved function with smallest (ignoring constant factors and trivial higher order terms) non-diminishing return -- its returns flatten too slowly to bound it's value.