I've noticed that with different words the words double, two, and duo work differently. Why so and how different are they? Are they interchangeable?

  • A double-barrel shotgun (why not a two-barrel or duo-barrel)
  • A duo-core processor (why not a double-core or a two-core)
  • A two-headed giant (why not a double-headed or a duo-headed)

Sometimes I also see the words pair and dual used in the same way.

  • A pair-legged creature.
  • A dual-color gradient.
  • 1
    You might even see dual as well. Apr 4, 2017 at 5:07
  • @LucianSava Yeh, I'll add it to the question. Apr 4, 2017 at 5:07
  • 1
    I've never seen "duo core", but "Dual-core" and "Core Duo". Dual is an adjective, duo a noun. Nor have I seen "pair-legged".
    – TimR
    Apr 4, 2017 at 12:05

2 Answers 2


double barrel
double-headed eagle

is used to signify a second but distinct copy, in a double barrel gun, both barrels are operated independently.

duo core
dynamic duo

implies there is some communication or coordination between the two parts so they act as a single unit even though there are two parts, in the case of duo core processors, there is load balancing. In the case of dynamic duo there is coordination between Batman and Robin.

two headed

it seems to be the tradition to usually "count" the number of body parts. It is also the case that the two heads act independently

Cerberus is a three headed dog
Hydra is a nine headed snake
Cyclops is one eyed giant
a three legged race

but of course there are exceptions

double-headed eagle

  • What about the other two. And are they all basically interchangeable? Apr 4, 2017 at 6:14
  • 2
    In your examples, not really. "Double barrel" is a set phrase, "duo barrel" is not. "Duo core" is a set technical phrase, they are all part of the jargon of describing what they are. You could possibly say "dual barrel" or "dual core" which would be understandable. Note that "duo core" is a branding name by Intel for their "dual processor".
    – Peter
    Apr 4, 2017 at 6:23
  • What about pair? Apr 4, 2017 at 6:48

I think this can help. double, duo, two, Each of these three words means "two". But relation between "one" and "one" in each one of them is different.

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