I was a truck driver for seven years in the United States. My understanding was that the term semi comes from the most basic definition meaning partial or incomplete.
When driving a road tractor without the trailer, the truck would actually NOT stop as fast, because the laws of physics push the vast majority of the truck's weight onto the steer tires when braking... So, ironically a tractor which is incomplete (or semi complete) takes longer to stop then a tractor which is complete with its trailer.
This is true because when you have a trailer with a load, you have the weight of the load keeping pressure on 18 wheels which with the tractor, trailer combination together has 5 axles, which have 10 drum brakes stopping capacity.
If you ever watch a truck driving without its trailer you will notice its rear drive tires bob up and down... especially when not on a smooth road. Hence truck driver's call the tractor... which is incomplete and NOT as safe without its trailer, a "bob tail"... because while going down the road, it's back end or tail is bobbing up and down.
So, on the CB... other truckers either call a truck without its trailer a bob tail a bob tail or a semi... meaning the truck was incomplete. In my 7 years of truck driving I have never heard the trailer called a semi...
I have heard a road tractor called: a tractor, big truck,
a ten wheeler, rig, but most often a "bob tail" or just a "semi truck". My understanding has always been the tractor is called a "semi" because it was incomplete, and NOT as safe to drive without the trailer.
I came on this web site because my brother in law told me he looked up "semi" in the dictionary and that I was wrong. He claimed the dictionary referred to the trailer as the "semi". So, I want to correct myself if I am wrong. Hence, I came here to do research... and tell what I know as an experienced driver of 18 wheelers.
Which still makes sense... the trailer is also incomplete without a tractor. I guess actually even more so because it can't even move without the tractor's tires to complete it.
Of course, for several years it has driven me nuts when a news reporter says a "semi" has overturned on the interstate... and in the same breath say, it will take hours to clean up as crews are unloading the trailer by hand because either way, it is incorrect to call a tractor with its trailer a semi because "semi" means incomplete... and when they are both together they are complete and hence no longer "semi".
Granted, the misnomer "semi" the reporter uses, is so over misused that the average radio listener accepts the incorrect term as normal vernacular. I guess the reporter uses "semi truck"... so people know it is an 18 wheeler or road tractor. Again, this gets on my nerves because either way, neither the tractor, nor the trailer are "semi" (incomplete) when they are attached to each other.
So, the bottom line is: If the tractor is attached to a trailer you can no longer "correctly" call the combination a semi. It has now become a tractor (meaning to pull) and a trailer (which means to be pulled behind).
So, from my perspective, I have always called my road tractor a "semi" truck, because I know it is semi complete without its trailer and I have to use extra caution and diligence when needing to stop, to keep from skidding.
My brother in law caused me to realize... the trailer is also "semi" complete without its tractor to pull it where it needs to go.
I will look into this deeper and let you know what I find. Thanks for reading.
One Hoof
Response last updated by gtho4 on Sep 10 2016.
Jan 02 2011, 7:14 AM