The Jargon File (version 4.4.7, 29 Dec 2003):

TOPS-20
 /tops?twen'tee/, n.

    See TWENEX.


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

TWENEX
TOPS-20

    /twe'neks/ The TOPS-20 operating system
   by DEC - the second proprietary OS for the PDP-10 -
   preferred by most PDP-10 hackers over TOPS-10 (that is, by
   those who were not ITS or WAITS partisans).  TOPS-20 began
   in 1969 as Bolt, Beranek & Newman's TENEX operating system
   using special paging hardware.  By the early 1970s, almost all
   of the systems on the ARPANET ran TENEX.  DEC purchased the
   rights to TENEX from BBN and began work to make it their own.
   The first in-house code name for the operating system was
   VIROS (VIRtual memory Operating System); when customers
   started asking questions, the name was changed to SNARK so DEC
   could truthfully deny that there was any project called VIROS.
   When the name SNARK became known, the name was briefly
   reversed to become KRANS; this was quickly abandoned when
   someone objected that "krans" meant "funeral wreath" in
   Swedish (though some Swedish speakers have since said it means
   simply "wreath"; this part of the story may be apocryphal).

   Ultimately DEC picked TOPS-20 as the name of the operating
   system, and it was as TOPS-20 that it was marketed.  The
   hacker community, mindful of its origins, quickly dubbed it
   TWENEX (a contraction of "twenty TENEX"), even though by this
   point very little of the original TENEX code remained
   (analogously to the differences between AT&T V6 Unix and BSD).
   DEC people cringed when they heard "TWENEX", but the term
   caught on nevertheless (the written abbreviation "20x" was
   also used).  TWENEX was successful and very popular; in fact,
   there was a period in the early 1980s when it commanded as
   fervent a culture of partisans as Unix or ITS - but DEC's
   decision to scrap all the internal rivals to the VAX
   architecture and its relatively stodgy VMS OS killed the
   DEC-20 and put a sad end to TWENEX's brief day in the sun.
   DEC attempted to convince TOPS-20 users to convert to VMS,
   but instead, by the late 1980s, most of the TOPS-20 hackers
   had migrated to Unix.

   [Jargon File]

   (1995-04-01)