Trunks

Why do they call swimming trunks,trunks ? With spring just around the corner I heard an advertisement for these. I never really paid attention before as I usually refer to them as a swim suit. Another curious name for them. Not much of a suit is it. You would look real silly wearing a tie with that suit. I have a pair of swim trunks for use in pools. That's another thing,why are they a pair ? Only have one of them. I can understand a pair of socks but a pair of trunks ? Would a one legged man wear a pair ? Why don't women wear swimming trunks ? They always wear suits. Their suits cover up their trunks or at least a portion of it so calling them trunks would make sense. Sorta.
There are other trunks as well. Tree trunks,trunks for storing things and a trunk in your car. Now calling a tree trunk a trunk makes perfect sense. Like the trunk of your body it houses the vital organs of the tree and has limbs on it just like us. Now the other trunks I'm not sure about. Were the first storage trunks actual trunks of trees ? Hollowed out closets in the forrest ? A place to store extra fig leaves because you just know Eve had more than one outfit. Later on did they cut them down and bring them inside the cave ? Something to think about. The trunk on your car is a place to store things too. We all keep stuff in there. 
So now I've reached a point were I think I figured this out. The answer has been there all along. Why do we call them swimming trunks ? Because we store junk in our trunks ! Don't touch my junk !