The Collaborative International Dictionary of English v.0.48:

octothorp \oc"to*thorp\, octothorpe \oc"to*thorpe\, n. [octo-
   eight + thorp Etymology of thorp uncertain. (ca. 1965). See
   quote below. Possibly derived from octalthorpe or octotherp
   (once used by the Bell System?).]
   A typographic symbol (#) having two vertical lines
   intersected by two horizontal lines. It is also called the
   crosshatch, hash, numeral sign and number sign; in
   the U. S. it is commonly called the pound sign, especially
   to designate the symbol as used on digital telephone dials,
   but this can be confusing to Europeans who think of the pound
   sign as the symbol for the British pound. It is commonly used
   as a symbol for the word number; as in #36 (meaning: number
   thirty-six).
   [PJC]

         octothorp
         Otherwise known as the numeral sign. It has also been
         used as a symbol for the pound avoirdupois, but this
         usage is now archaic. In cartography, it is also a
         symbol for village: eight fields around a central
         square, and this is the source of its name. Octothorp
         means eight fields.
                                                  --Robert
                                                  Bringhurst
                                                  (The Elements
                                                  of Typographic
                                                  Style (2d
                                                  edition,
                                                  1996), Hartley
                                                  & Marks,
                                                  Publishers,
                                                  Point Roberts,
                                                  WA; Vancouver,
                                                  BC, Canada, p.
                                                  282)
   [Joel Neely]

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

hash character
octothorpe

    "#", ASCII character 35.

   Common names: number sign; pound; pound sign; hash; sharp;
   crunch; hex; INTERCAL: mesh.  Rare: grid; crosshatch;
   octothorpe; flash; ITU-T: square, pig-pen; tictactoe;
   scratchmark; thud; thump; splat.

   The pronunciation of "#" as "pound" is common in the US but a
   bad idea; Commonwealth Hackish has its own, rather more
   apposite use of "pound sign" (confusingly, on British
   keyboards the pound graphic happens to replace "#"; thus
   Britishers sometimes call "#" on a US-ASCII keyboard "pound",
   compounding the American error).  The US usage derives from an
   old-fashioned commercial practice of using a "#" suffix to tag
   pound weights on bills of lading.  The character is usually
   pronounced "hash" outside the US.

   The name "octothorpe" was made up by a Bell Labs supervisor,
   Don Macpherson.

   Octothorpe story
   (http://sigtel.com/tel_tech_octothorpe.html).

   (2003-07-05)