deficient, inferior, substandard

from The Collaborative International Dictionary of English v.0.48
nonstandard \nonstandard\, non-standard \non-standard\adj.
   1. varying from or not adhering to a standard; as,
      nonstandard windows; envelopes of nonstandard sizes;
      non-standard lengths of board cost more per foot. Opposite
      of {standard}. [Narrower terms: {deficient, inferior,
      substandard}]

   Syn: nonstandard.
        [WordNet 1.5]

   2. (Linguistics) Not conforming to the language usage of a
      prestige group within a community; as, a nonstandard
      dialect is one used by uneducated speakers or socially
      disfavored groups. Opposite of {standard}.
      [WordNet 1.5]
    

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