The compound 'underway' originated in the nautical lexicon of the 18th century. It literally described a ship that had weighed anchor and was 'under way', meaning it was moving along its course or path through the water, no longer stationary. The preposition 'under' here carries an older sense of 'in the process of' or 'subject to', as seen in terms like 'under construction'. Over time, the term moved from its specific maritime context into general usage. It now broadly describes any project, process, or journey that has commenced and is currently in progress, retaining the core idea of being on a figurative path or course.

Structure: under + way - under (Old English): A preposition/adverb meaning 'beneath, below, in a lower position'. - way (Old English): A noun meaning 'path, road, course of travel'.