Source : Webster's Revised Unabridged Dictionary (1913)

      Both Jews and Gentiles . . . are all under sin. --Rom.
                                                  iii. 9.

      That led the embattled seraphim to war Under thy conduct.
                                                  --Milton.

      Who have their provand Only for bearing burdens, and sore
      blows For sinking under them.               --Shak.
      (b) Denoting relation to something that exceeds in rank or
          degree, in number, size, weight, age, or the like; in
          a relation of the less to the greater, of inferiority,
          or of falling short.

                Three sons he dying left under age. --Spenser.

                Medicines take effect sometimes under, and
                sometimes above, the natural proportion of their
                virtue.                           --Hooker.

                There are several hundred parishes in England
                under twenty pounds a year.       --Swift.

                It was too great an honor for any man under a
                duke.                             --Addison.

   Note: Hence, it sometimes means at, with, or for, less than;
         as, he would not sell the horse under sixty dollars.

               Several young men could never leave the pulpit
               under half a dozen conceits.       --Swift.
      (c) Denoting relation to something that comprehends or
          includes, that represents or designates, that
          furnishes a cover, pretext, pretense, or the like; as,
          he betrayed him under the guise of friendship;
          Morpheus is represented under the figure of a boy
          asleep.

                A crew who, under names of old renown . . .
                abused Fanatic Egypt.             --Milton.

                Mr. Duke may be mentioned under the double
                capacity of a poet and a divine.  --Felton.

                Under this head may come in the several contests
                and wars betwixt popes and the secular princes.
                                                  --C. Leslie.
      (d) Less specifically, denoting the relation of being
          subject, of undergoing regard, treatment, or the like;
          as, a bill under discussion.

                Abject and lost, lay these, covering the flood,
                Under amazement of their hideous change.
                                                  --Milton.

   {Under arms}. (Mil.)
      (a) Drawn up fully armed and equipped.
      (b) Enrolled for military service; as, the state has a
          million men under arms.

   {Under canvas}.
      (a) (Naut.) Moved or propelled by sails; -- said of any
          vessel with her sail set, but especially of a steamer
          using her sails only, as distinguished from one under
          steam. Under steam and canvas signifies that a vessel
          is using both means of propulsion.
      (b) (Mil.) Provided with, or sheltered in, tents.

   {Under fire}, exposed to an enemy's fire; taking part in a
      battle or general engagement.

   {Under foot}. See under {Foot}, n.

   {Under ground}, below the surface of the ground.

   {Under one's signature}, with one's signature or name
      subscribed; attested or confirmed by one's signature. Cf.
      the second Note under {Over}, prep.

   {Under sail}. (Naut.)
      (a) With anchor up, and under the influence of sails;
          moved by sails; in motion.
      (b) With sails set, though the anchor is down.
      (c) Same as {Under canvas}
      (a), above. --Totten.

   {Under sentence}, having had one's sentence pronounced.

   {Under the breath}, with low voice; very softly.

   {Under the lee} (Naut.), to the leeward; as, under the lee of
      the land.

   {Under the rose}. See under {Rose}, n.

   {Under water}, below the surface of the water.

   {Under way}, or {Under weigh} (Naut.), in a condition to make
      progress; having started.

Source : WordNet®

under way
     adv : in motion; set in motion; "the ship got under way"