As I was driving down the highway in the countryside recently, I had to stop for a pair of ducks taking their huge flock of babies across the road. (For some reason there are lots of baby ducks around this year.) After I moved on, I flashed my headlights at oncoming cars to warn them to take care and to be alert for something surprising on the road.
Continuing my journey, I wondered if anything else would dart out of the long grasses that came right to the edge of the road. (Bushfire season coming and the grasses haven't been mown!) The word start came to my mind. Would a rabbit start from the undergrowth and would I be able to stop safely to avoid hitting it?
Start. Hmmm... I wondered about the connection of an animal starting and the word startle.
So, off to etymology.com to have a look.
And I found that around 1300 the word startle meant to run to and fro. It was an intransitive verb. And a frequentative form. That was a new concept to me. It means a verb dealing with a repeated action.
From the 1520s it is recorded with the meaning of 'move suddenly in surprise or fear'. That was the meaning that had popped into my head as I drove along. From the 1590s we see the transitive meaning of 'frighten suddenly'.
And it all relates back to the word start, as I thought. The original concept, in Old English, was to leap up, to move or spring suddenly. By the 1660s it is recorded in the sense of 'cause to begin acting or operating.'
I wonder why the old-fashioned meaning occurred to me when I was driving along? I guess I've read it somewhere and it has stuck, as odd words and unusual phrases have a habit of doing. It's going to bother me until I think of somewhere I might have read it.
Ooh, now I think I'm in love with frequentative word forms. Here's a site that discusses them.