The Collaborative International Dictionary of English v.0.48:

First-hand \First"-hand`\, a.
   Obtained directly from the first or original source; hence,
   without the intervention of an agent; -- of information; as,
   a firsthand report; firsthand information; firsthand
   knowledge.

   Syn: direct, original.
        [1913 Webster]

              One sphere there is . . . where the apprehension
              of him is first-hand and direct; and that is the
              sphere of our own mind.             --J.
                                                  Martineau.
        [1913 Webster]

WordNet (r) 3.0 (2006):

firsthand
    adv 1: from the original source; directly; "I heard this story
           firsthand" [syn: firsthand, at first hand]
    adj 1: received directly from a source; "firsthand information"

Moby Thesaurus II by Grady Ward, 1.0:

84 Moby Thesaurus words for "firsthand":
   absolute, adducible, admissible, attestative, attestive, authentic,
   avant-garde, based on, callow, certain, circumstantial, conclusive,
   convincing, creative, cumulative, damning, decisive, determinative,
   dewy, documentary, documented, ever-new, evergreen, evidential,
   evidentiary, ex parte, eye-witness, factual, final, fledgling,
   founded on, fresh, green, grounded on, hearsay, imaginative,
   immature, immediate, implicit, incontrovertible, indicative,
   indisputable, intact, irrefutable, irresistible, maiden, maidenly,
   material, neoteric, nestling, new, novel, nuncupative, original,
   overwhelming, presumptive, primary, pristine, probative, raw,
   reliable, revolutionary, sempervirent, significant, suggestive,
   sure, symptomatic, telling, unbeaten, underived, undeveloped,
   unfledged, unhandled, unique, untouched, untried, untrodden,
   unused, valid, vernal, virgin, virginal, weighty, young