unimpressionable

from WordNet (r) 3.0 (2006)

unimpressionable
    adj 1: not sensitive or susceptible to impression; "an
           unimpressionable mind" [ant: {impressible},
           {impressionable}, {waxy}]

from The Collaborative International Dictionary of English v.0.48

Unimpressionable \Unimpressionable\
   See {impressionable}.

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