I find that I am rarely ambivalent about a word, and rivulet is no exception. I like this word. I use this word, even though it is limited in its usage. So, let's get started:
Now, even before I check the etymology of this word, doesn't rivulet look like it means "little river"? "Rivu" looks like it derives from some word like "river" and "et" is the diminutive ending for "little" ("et" for masculine gender nouns and "ette" for feminine gender nouns). So, it should come as no surprise that rivulet derives from the Latin "rivulus", a diminutive of "rivus" for river. That's it. Nothing special about the etymology to the current usage. Still the same little river. What is fun about this word is the usage. Of course, the torrential rains made every rivulet into a raging surge of water. Or after washing her car, the rain dripped off in myriad rivulets. Her tears ran down her face like rivulets. Bad wine doesn't have "legs" but "rivulets". So, clearly, rivulet can be used with the actual stream, water in other forms, and things that act like water (running, dripping, flowing). But that's too easy. Lacking a good vocabulary, his anger did not so much pour from his mouth as a stream, but rather as a rivulet. Maybe. Comments on her blog were barely rivulets. Possibly, and accurate too. Plaintiff's counsel's argument had all the force of a rivulet. hehehe. Life is like a rivulet... Ok, that was a bad attempt at humor. Clearly, rivulet can work with other intangibles that may be analogized (metaphorized???) to water, and not even just for sarcastic value! Now, just as an aside, rivulet is only a noun. Her ideas were rivuleting or his sweat rivuleted down his back? I won't even begin to discuss how wrong those are. It is a fine noun and has plenty of opportunity to be used just as the noun that it is. Let the usages of rivulet flow!