i call them henleys , isnt that the right name??, my cousins call it skivvies ( sounds cooler) , actually they were popular in the 70s , but now stores like AE and AF sell them by the truckloads and call them long sleeve tees lol , they arent !
I know it's originally a label, so maybe they made henleys too, but I think skivvies is usually used in the meaning "underwear".
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According to wikipedia the name henley comes from this type of collarless shirt with a few buttons in the front being the traditional uniform of rowers in the English city of Henley-on-Thames.