The Collaborative International Dictionary of English v.0.48:

Sickly \Sick"ly\, adv.
   In a sick manner or condition; ill.
   [1913 Webster]

         My people sickly [with ill will] beareth our marriage.
                                                  --Chaucer.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sickly \Sick"ly\, v. t.
   To make sick or sickly; -- with over, and probably only in
   the past participle. [R.]
   [1913 Webster]

         Sicklied o'er with the pale cast of thought. --Shak.
   [1913 Webster]

         Sentiments sicklied over . . . with that cloying
         heaviness into which unvaried sweetness is too apt to
         subside.                                 --Jeffrey.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sickly \Sick"ly\, a. [Compar. Sicklier; superl. Sickliest.]
   1. Somewhat sick; disposed to illness; attended with disease;
      as, a sickly body.
      [1913 Webster]

            This physic but prolongs thy sickly days. --Shak.
      [1913 Webster]

   2. Producing, or tending to, disease; as, a sickly autumn; a
      sickly climate. --Cowper.
      [1913 Webster]

   3. Appearing as if sick; weak; languid; pale.
      [1913 Webster]

            The moon grows sickly at the sight of day. --Dryden.
      [1913 Webster]

            Nor torrid summer's sickly smile.     --Keble.
      [1913 Webster]

   4. Tending to produce nausea; sickening; as, a sickly smell;
      sickly sentimentality.
      [1913 Webster]

   Syn: Diseased; ailing; infirm; weakly; unhealthy; healthless;
        weak; feeble; languid; faint.
        [1913 Webster]

WordNet (r) 3.0 (2006):

sickly
    adj 1: unhealthy looking [syn: sallow, sickly]
    2: somewhat ill or prone to illness; "my poor ailing
       grandmother"; "feeling a bit indisposed today"; "you look a
       little peaked"; "feeling poorly"; "a sickly child"; "is
       unwell and can't come to work" [syn: ailing, indisposed,
       peaked(p), poorly(p), sickly, unwell, under the
       weather, seedy]

Moby Thesaurus II by Grady Ward, 1.0:

110 Moby Thesaurus words for "sickly":
   achromatic, achromic, ailing, anemic, ashen, ashy, bled white,
   bloodless, cachectic, cadaverous, chloranemic, cloying, colorless,
   cranky, dead, deadly pale, deathly pale, debilitated, delicate,
   dim, dimmed, dingy, discolored, diseased, donsie, down, drained,
   drawn, dull, enervated, etiolated, exhausted, exsanguinated,
   exsanguine, exsanguineous, faded, failing, faint, fallow, feeble,
   flat, frail, ghastly, gray, haggard, healthless, hueless,
   hypochromic, in poor health, indisposed, infirm, insalubrious,
   insipid, invalid, lackluster, languishing, leaden, livid, low,
   lurid, lusterless, mat, maudlin, mawkish, mealy, mean, moribund,
   morose, muddy, mushy, neutral, noisome, noxious, off-color, offish,
   pale, pale as death, pale-faced, pallid, pasty, peaked, peaking,
   peaky, pimping, poorly, puny, reduced, reduced in health, run-down,
   sallow, sick, sickish, tallow-faced, toneless, uncolored,
   unhealthful, unhealthy, unsound, valetudinarian, valetudinary, wan,
   washed-out, watery, waxen, weak, weakened, weakly, whey-faced,
   white, with low resistance