The Collaborative International Dictionary of English v.0.48:

Peaked \Peaked\ (p[=e]kt or p[=e]k"[e^]d), a.
   1. Pointed; ending in a point; as, a peaked roof.
      [1913 Webster]

   2. (Oftener p[=e]k"[e^]d) Sickly; not robust. [Colloq.]
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Peak \Peak\, v. i. [imp. & p. p. Peaked (p[=e]kt); p. pr. &
   vb. n. Peaking.]
   1. To rise or extend into a peak or point; to form, or appear
      as, a peak.
      [1913 Webster]

            There peaketh up a mighty high mount. --Holand.
      [1913 Webster]

   2. Hence: To achieve a maximum of numerical value, intensity
      of activity, popularity, or other characteristic, followed
      by a decline; as, the stock market peaked in January; his
      performance as a pitcher peaked in 1990; sales of the XTX
      model peaked at 20,000 per year.
      [PJC]

   3. To acquire sharpness of figure or features; hence, to look
      thin or sickly. "Dwindle, peak, and pine." --Shak.
      [1913 Webster]

   4. [Cf. Peek.] To pry; to peep slyly. [archaic] --Shak.
      [1913 Webster]

   Peak arch (Arch.), a pointed or Gothic arch.
      [1913 Webster]

WordNet (r) 3.0 (2006):

peaked
    adj 1: 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]
    2: having or rising to a peak; "the peaked ceiling"; "the
       island's peaked hills"