> Who created the "cat" command and did they have the
> word "catenate" or "concatenate" in their heads?

Ken Thompson wrote "cat" for the PDP-7, with "concatenate" in
mind. The cat(1) page in the v1 manual is titled, "concatenate (or
print) files". Only later did someone in Research--I don't know
who--remark on the existence of the shorter synonym. It was
deliberately adopted in v7, perhaps because it better mirrored
the command name. 

But brevity is the defensible argument for "catenate", while
familiarity boosts "concatenate". It stll takes some conscious
effort for me to use the former, However, I sense sinister
vibes in "concatenate", driven by the phrase "concatenation
of events", which often is used to explain misfortune.

Doug