Source : Webster's Revised Unabridged Dictionary (1913)

Chronic \Chron"ic\, a. [L. chronicus, Gr. ? concerning time,
   from ? time: cf. F. chronique.]
   1. Relating to time; according to time.

   2. Continuing for a long time; lingering; habitual.

   {Chronic disease}, one which is inveterate, of long
      continuance, or progresses slowly, in distinction from an
      acute disease, which speedly terminates.

Source : WordNet®

chronic
     adj 1: being long-lasting and recurrent or characterized by long
            suffering; "chronic indigestion"; "a chronic shortage
            of funds"; "a chronic invalid" [ant: {acute}]
     2: having a habit of long standing; "a chronic smoker" [syn: {confirmed},
         {habitual}, {inveterate(a)}]