The Collaborative International Dictionary of English v.0.48:

Bliss \Bliss\ (bl[i^]s), n.; pl. Blisses (bl[i^]s"[e^]z). [OE.
   blis, blisse, AS. blis, bl[imac][eth]s, fr. bl[imac][eth]e
   blithe. See Blithe.]
   Orig., blithesomeness; gladness; now, the highest degree of
   happiness; blessedness; exalted felicity; heavenly joy.
   [1913 Webster]

         An then at last our bliss
         Full and perfect is.                     --Milton.
   [1913 Webster]

   Syn: Blessedness; felicity; beatitude; happiness; joy;
        enjoyment. See Happiness.
        [1913 Webster]

WordNet (r) 3.0 (2006):

bliss
    n 1: a state of extreme happiness [syn: bliss, blissfulness,
         cloud nine, seventh heaven, walking on air]

The Free On-line Dictionary of Computing (19 January 2023):

Basic Language for Implementation of System Software
BLISS

    (BLISS, or allegedly, "System Software
   Implementation Language, Backwards") A language designed by
   W.A. Wulf at CMU around 1969.

   BLISS is an expression language.  It is block-structured,
   and typeless, with exception handling facilities,
   coroutines, a macro system, and a highly optimising
   compiler.  It was one of the first non-assembly languages
   for operating system implementation.  It gained fame for its
   lack of a goto and also lacks implicit dereferencing: all
   symbols stand for addresses, not values.

   Another characteristic (and possible explanation for the
   backward acronym) was that BLISS fairly uniformly used
   backward keywords for closing blocks, a famous example being
   ELUDOM to close a MODULE.  An exception was BEGIN...END though
   you could use (...) instead.

   DEC introduced the NOVALUE keyword in their dialects to allow
   statements to not return a value.

   Versions: CMU BLISS-10 for the PDP-10; CMU BLISS-11,
   BLISS-16, DEC BLISS-16C, DEC BLISS-32, BLISS-36 for
   VAX/VMS, BLISS-36C.

   ["BLISS: A Language for Systems Programming", CACM
   14(12):780-790, Dec 1971].

   [Did the B stand for "Better"?]

   (1997-03-01)