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“PIN Number” — why do we say it?

Assume we abbreviate "Orthogonal Multi-user Channel" as OMC. Is it correct to use the phrase "OMC channel" since channel is already contained in OMC?

  • But OMC is already an abbreviation for the osteomeatal complex. So as people who know about these things will be perfectly well aware, there's no redundancy in saying "[the] four paranasal sinuses are interconnected through the osteomeatal complex (OMC) channel.". Mar 6, 2012 at 3:09
  • 2
    The language legislature has not yet ruled it incorrect. Perhaps you should send them a petition.
    – GEdgar
    Mar 6, 2012 at 3:46
  • @GEdgar: How can I do the petition?
    – Helium
    Mar 6, 2012 at 3:48
  • It should go to The Academy. Mar 6, 2012 at 3:58

1 Answer 1


This is commonly referred to as RAS Syndrome, or Redundant Acronym Syndrome Syndrome. Other examples of this are ATM Machine (Automated Teller Machine Machine) and PIN Number (Personal Identification Number Number).

This is not technically correct, but it happens pretty often.

  • Don't forget TLA (Three-Letter Acronym), and ETLA (Extended Three-Letter Acronym, used for acronyms with four letters). Mar 6, 2012 at 2:26
  • @Jim: +1; spot on. Every now and then, I run across someone who gets really irked by redundancies such as "VIN Number" and "CAC Card." It seems to happen rather naturally, however, and I've never had a problem with it.
    – J.R.
    Mar 6, 2012 at 3:45
  • According to which technical specification is it "not technically correct"?
    – Colin Fine
    Mar 6, 2012 at 14:57

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