The Collaborative International Dictionary of English v.0.48:

hard-bitten \hard-bitten\ hard-boiled \hard-boiled\adj.
   not given to sentimentality or gentleness; -- of people; as,
   a hard-bitten character.

   Syn: pugnacious, tough.
        [WordNet 1.5 +PJC]

The Collaborative International Dictionary of English v.0.48:

hard-boiled \hard-boiled\ adj.
   1. same as hard-bitten.

   Syn: hard-bitten, pugnacious.
        [WordNet 1.5]

   2. emotionally hardened; -- used of persons.

   Syn: callous, case-hardened, hardened.
        [WordNet 1.5]

   3. cooked until the yolk is solid; -- used of eggs; as, a
      breakfast of pancakes and hard-boiled eggs.
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

hard-boiled
    adj 1: tough and callous by virtue of experience [syn: hard-
           bitten, hard-boiled, pugnacious]
    2: used of persons; emotionally hardened; "faced a case-hardened
       judge" [syn: case-hardened, hardened, hard-boiled]
    3: (eggs) cooked until the yolk is solid