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.
      [1913 Webster]

            As loose it [the sail] flagged around the mast. --T.
                                                  Moore.
      [1913 Webster]

   2. To droop; to grow spiritless; to lose vigor; to languish;
      as, the spirits flag; the strength flags.
      [1913 Webster]

            The pleasures of the town begin to flag. --Swift.

   Syn: To droop; decline; fail; languish; pine.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Flagging \Flag"ging\, n.
   A pavement or sidewalk of flagstones; flagstones,
   collectively.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Flagging \Flag"ging\, a.
   Growing languid, weak, or spiritless; weakening; delaying. --
   Flag"ging*ly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

flagging
    adj 1: weak from exhaustion [syn: drooping, flagging]
    n 1: flagstones collectively; "there was a pile of flagging
         waiting to be laid in place"
    2: a walk of flagstones; "the flagging in the garden was quite
       imaginative"

Moby Thesaurus II by Grady Ward, 1.0:

132 Moby Thesaurus words for "flagging":
   ambling, cautious, circumspect, claudicant, coming apart, cracking,
   crawling, creeping, creeping like snail, crumbling, debilitated,
   decadent, declining, degenerate, deliberate, deteriorating,
   disintegrating, draining, drooping, droopy, dwindling, easy,
   ebbing, effete, enervated, enfeebled, fading, fagged, failing,
   faint, fainting, falling, faltering, fatigued, feeling faint,
   foot-dragging, footsore, fragmenting, frazzled, gentle,
   going to pieces, good and tired, gradual, halting, hobbled,
   hobbling, idle, indolent, jaded, languid, languishing, languorous,
   lazy, leisurely, limping, lumbering, marcescent, moderate, pining,
   poking, poky, ready to drop, regressive, relaxed, reluctant,
   retrograde, retrogressive, run ragged, run-down, sagging,
   sauntering, seedy, shriveling, shuffling, sinking, slack, sliding,
   slipping, slothful, slow, slow as death, slow as molasses,
   slow as slow, slow-crawling, slow-foot, slow-going, slow-legged,
   slow-moving, slow-paced, slow-poky, slow-running, slow-sailing,
   slow-stepped, sluggish, slumping, snail-paced, snaillike,
   staggering, strolling, subsiding, tabetic, tentative, tired,
   tired-winged, toddling, toilworn, tortoiselike, tottering,
   trudging, turtlelike, unhurried, unrefreshed, unrestored, waddling,
   waning, wasting, way-weary, wayworn, weak, weakened, wearied,
   weariful, weary, weary-footed, weary-laden, weary-winged,
   weary-worn, wilting, withering, worn, worn-down, worsening