Trepidation (DD definition link)
Well, from "agitated, restless, disturbed" we get "state of dread or alarm, nervous agitation, apprehension, fright". It's not an impossible stretch to get from agitated to nervous agitation, but certainly there are other conditions which cause agitation other than being nervous. I can easily think of anger, medication, too much noise, sleep deprivation, Plaintiff's counsel.... The idea that one who is restless also doesn't derive solely from nervousness. I am frequently restless when I am bored and have nothing to do, as when I am waiting for time to pass before I can do something, or for something to happen before I can respond. I am hardly nervous or afraid, but I may be agitated (I may also be agitating to others as they watch me pace and twitter). Disturbed is just to vague to get "nervous" from any more than any other modifier. I regularly describe some movies as "disturbed", not "disturbing" because I believe the movie is so inherently off kilter that it is the cause of its own problem, and not that it just might have that effect on viewers (see Leaving Las Vegas, Hostel, Trainspotting). These movies are hardly nervous, nor do they induce nervousness, and aside from the horror entry, the others don't induce dread, alarm, apprehension or fright, as much as disgust or depression. So, how do we get the nervous fear aspect from mere hype? Because, DD's etymology is incorrect! OED gives the Latin for "tredipus" as scared or alarmed and "trepidare" as to hurry, bustle, be agitated or alarmed. So that gets us the fright, restless and state of alarm elements, but not entirely the apprehension, nervous or dread since the latter are anticipatory of the states of being in fear and/or don't relate to mere "hustle and bustle". It is not unreasonable to tack on the preceding emotional states, but as we know in the law, you can be battered without being assaulted (just remember that the next time you think about drawing on someone while she is asleep). So certainly, you can be put in a state of fear without being nervous about being afraid. Someone jumps out in front of you with a gun, regardless of whether it was a dark alley or a dark and stormy night. Why does the definition of trepidation include the anticipatory states? Because, DD's definitions are incorrect! OED defines the relevant entry solely as "tremulous agitation; confused hurry or alarm; confusion; flurry; perturbation". Most these are similar to the DD definition: agitation, alarm, flurry (= restlessness). Except now we have element of shaking and confusion, which ironically, are effects of being scared. He scared her with the gun and then she shook with fear, unable to think straight for several seconds. Not everyone has to be that scared that they shake and are confused after being scared. Fight or flight allows for other responses. But trepidation does have an archaic usage for trembling, which may derive from either the extreme response to fear or from the perception of the bustling and agitation. More importantly, however, the OED definition brings into focus that the use of the word, although still not the etymology, is on the movement, not the emotional state which may have caused the movement. So, it appears that trepidation refers not just to the state of fear, but also restless energy. Funny, though how despite the convoluted definitions, the usage of the word probably remains the most accurate.
Either way, I'll take a strict and narrow usage of trepidation for only in the state of fear, alarm or agitation, and stay away from the preceding or antecedent states, and try to remember that it really should describe movement. Her trepidation about going to rehearsals unprepared and being singled out for an inadvertent solo motivated her to practice 3 hours that day. That works for the limited definition from DD and our understanding of common usage, but doesn't work with the OED definition, relative to the motion meaning. His trepidation immediately abated when he arrived too early for the hearing. Yeah, maybe, but even thought it may have meant the bustle and flurry elements, it still reads like fear. In her trepidation at what the police wanted, she could barely open the door. Still just fear.
Ed. note: DD normally gives reasonable etymologies, and certainly for average understanding and usage of words, its definitions are fine. But that's not what this forum is about. I don't want to just think I know what a word means and how to use it. I want to know why that knowledge is correct, and I have to follow my instincts when the analysis just isn't making any kind of sense. Thank you for your patience.