The Collaborative International Dictionary of English v.0.48:

HN \HN\ n.
   a colorless explosive liquid that is volatile, poisonous, and
   foul-smelling.

   Syn: hydrazoic acid, azoimide.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

HN
    n 1: a colorless explosive liquid that is volatile and poisonous
         and foul-smelling [syn: hydrazoic acid, azoimide,
         hydrogen azide, HN]

The Free On-line Dictionary of Computing (30 December 2018):

hn

    The country code for Honduras.

   (1999-01-27)