WordWeb Online

1. Unhealthy looking
   - sallow, peaky [Brit, informal]
    
2. Somewhat ill, feeling or being in bad health
   "a sickly child";
   - ailing, indisposed, peaked, poorly, unwell, under the weather [informal], seedy [archaic], off-colour [Brit, informal], out of sorts [informal], grotty [Brit, informal], crook [Austral, NZ, informal]

Derived forms: sicklier, sickliest

See also: ill, sick, unhealthy