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