late Middle English: from Old French train (masculine), traine (feminine), from trahiner (verb), from Latin trahere ‘pull, draw’. Early noun senses were ‘trailing part of a robe’ and ‘retinue’; the latter gave rise to ‘line of traveling people or vehicles’, later ‘a connected series of things’. The early verb sense ‘cause a plant to grow in a desired shape’ was the basis of the sense ‘instruct’.