illative: [adjective]

1. Of, relating to, or of the nature of an illation.
2. Expressing or preceding an inference. Used of a word.
3. Of, relating to, or being a grammatical case indicating motion toward or into in some languages, as in Finnish Helsinkiin, ”to Helsinki.”

(American Heritage Dictionary via Dictionary.com)This word also seen in Five Days in London: May 1940 by John Lukacs, in this context:

“Yet the immediate effect of these speeches [of Churchill’s] on the British people was limited. Their effect was cumulative (or, to use Cardinal Newman’s favorite adjective, illative).”

It’s an interesting use, since in this context, illative implies a significant effect produced by a prior accumulation of insignificant impacts, whereas the dictionary definition suggests a subtler manipulation.