The Collaborative International Dictionary of English v.0.48:

Impenitent \Im*pen"i*tent\, a. [L. impaenitens; pref. im- not +
   paenitens penitens: cf. F. imp['e]nitent. See Penitent.]
   Not penitent; not repenting of sin; not contrite; of a hard
   heart. "They . . . died impenitent." --Milton. "A careless
   and impenitent heart." --Bp. Hall.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Impenitent \Im*pen"i*tent\, n.
   One who is not penitent. [R.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

impenitent
    adj 1: not penitent or remorseful [syn: impenitent,
           unrepentant, unremorseful] [ant: penitent,
           repentant]
    2: impervious to moral persuasion