The Jargon File, Version 4.0.0, 24 Jul 1996

The preface has gotten so long an intertwined that we moved it to the end
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The Jargon Lexicon
= A = =====
:abbrev: / -breev'/, / -brev'/ /n./ Common abbreviation for `abbreviation'.
:accumulator: /n. obs./ 1. Archaic term for a register. On-line use of it as a synonym for `register' is a fairly reliable indication that the user has been around for quite a while and/or that the architecture under discussion is quite old. The term in full is almost never used of microprocessor registers, for example, though symbolic names for arithmetic registers beginning in `A' derive from historical use of the term `accumulator' (and not, actually, from `arithmetic'). Confusingly, though, an `A' register name prefix may also stand for `address', as for example on the Motorola 680x0 family. 2. A register being used for arithmetic or logic (as opposed to addressing or a loop index), especially one being used to accumulate a sum or count of many items. This use is in context of a particular routine or stretch of code. The FOOBAZ routine uses A3 as an accumulator. 3. One's in-basket (esp. among old-timers who might use sense 1). You want this reviewed? Sure, just put it in the accumulator. (See {stack}.)
There is also a usage ACK? (from sense 1) meaning Are you there? , often used in email when earlier mail has produced no reply, or during a lull in {talk mode} to see if the person has gone away (the standard humorous response is of course {NAK} (sense 2), i.e., I'm not here ).
:Acme: /n./ The canonical supplier of bizarre, elaborate, and non-functional gadgetry — where Rube Goldberg and Heath Robinson shop. Describing some X as an Acme X either means This is {insanely great} , or, more likely, This looks {insanely great} on paper, but in practice it's really easy to shoot yourself in the foot with it. Compare {pistol}.
This term, specially cherished by American hackers and explained here for the benefit of our overseas brethren, comes from the Warner Brothers' series of Roadrunner cartoons. In these cartoons, the famished Wile E. Coyote was forever attempting to catch up with, trap, and eat the Roadrunner. His attempts usually involved one or more high-technology Rube Goldberg devices — rocket jetpacks, catapults, magnetic traps, high-powered slingshots, etc. These were usually delivered in large cardboard boxes, labeled prominently with the Acme name. These devices invariably malfunctioned in violent and improbable ways.