IST

from The Collaborative International Dictionary of English v.0.48

-ist \-ist\ ([i^]sh"[-u]*[i^]st). [Gr. ?: cf. F. -iste.]
   A noun suffix denoting an agent, or doer, one who practices,
   a believer in; as, theorist, one who theorizes; socialist,
   one who holds to socialism; sensualist, one given to
   sensuality.
   [1913 Webster]

from The Collaborative International Dictionary of English v.0.48

Is't \Is't\
   A contraction of is it.
   [1913 Webster]

from The Free On-line Dictionary of Computing (8 July 2008)

IST

   <company> {Imperial Software Technology}.

   (1995-10-12)

from V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006)

IST
       Immerse System Technology (VR)

from V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006)

IST
       Indian Standard Time [+0530] (TZ)

from V.E.R.A. -- Virtual Entity of Relevant Acronyms (June 2006)

IST
       Initial System Test