means A connected line of railway cars pulled along tracks; or, as a verb, to teach or condition someone or something into a skill or habit through repeated practice.

from From Old French 'train,' meaning the part that drags behind — a procession, a retinue, the trailing hem of a gown — built on the Latin 'trahere,' 'to pull or draw' (the same root that gives us 'tractor' and 'traction'). For centuries a 'train' was anything strung out and pulled along: a train of mules, a train of thought, the train of a bride's dress. When iron carriages began to be hauled in a line behind an engine, the old word was simply waiting for them. The 'teach' sense grew from the same pulling idea — you 'draw' a person or a plant into the desired shape, the way a gardener trains a vine along a wall.