I. adverb
Etymology: probably from Dutch onderweg, onderwege, from Middle Dutch onderwegen, onderwege, from onder between, among + wegen, wege, dative & accusative plural of wech way; akin to Old High German untar between, among and to Old High German wec way — more at inter- , way
1. : in motion : not at rest : not moored : not at anchor
2. : into motion from a standstill
an electric train gets under way rapidly
3. : in process of development : in progress toward completion : afoot
preparations for a big celebration were under way
before the discussion was well under way
II. adverb
1. of a ship or boat
a. : in motion through the water
b. : not at anchor : not made fast to the shore : not aground
2. : in motion along a course : in progress : on the way