The Collaborative International Dictionary of English v.0.48:

Flag \Flag\ (fl[a^]g), v. i. [imp. & p. p. Flagged (fl[a^]gd);
   p. pr. & vb. n. Flagging (fl[a^]g"g[i^]ng).] [Cf. Icel.
   flaka to droop, hang loosely. Cf. Flacker, Flag an
   ensign.]
   1. To hang loose without stiffness; to bend down, as flexible
      bodies; to be loose, yielding, limp.
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            As loose it [the sail] flagged around the mast. --T.
                                                  Moore.
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   2. To droop; to grow spiritless; to lose vigor; to languish;
      as, the spirits flag; the strength flags.
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            The pleasures of the town begin to flag. --Swift.

   Syn: To droop; decline; fail; languish; pine.
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