I’m sure somebody will come up with it minutes, but my brain is refusing to work.
When two words are pretty much always used together, like ‘bated breath’ or ‘free rein’
“Collocation” is probably the word you’re looking for. Though “stock phrase” or “set phrase,” as a subset of “expression,” is probably a more useful description in many cases. “Idiom” is not accurate for examples where the meaning of the phrase can be discerned from the meaning of the words without additional context.
No, it was a two word term. It was a type of cliche, I believe. I wish I could think of better examples.
Compound words ?
Fossilized term?
I don’t understand what you’re saying. “Bated” and “breath” are both very frequently used away from one another. “Free” and “rein” are also similarly quite often found apart.
The stuff you gave as examples are just stock phrases, or something.
I can’t remember the last time I’ve seen “bated” used without “breath.” i would agree about “free” and “rein”.
Really? Where else is ‘bated’ used?
I might have been thinking of ‘fixed expression’. I’m having a word moment about it.
Before “breath” or after “master”.
Actually, ‘cliche’ is the word you’re looking for.
I thought it was baited breath.
Learn something new everyday.
Bated is a perfectly good word… “His fears were bated when he found his daughter in the playground,” for example. In no way is it required to precede the word “breath.”
Not only that, but bated also refers to the flapping of wings, which is also where you’ll also see it used (although it just a homophone).
Not required, but as a practical matter almost no modern English speaker uses it for any purpose other then to preface the word “breath”. Googling, I can only find one use of the word that isn’t in front of breath, and that case looks like it might be a mis-spelling of “baited”.
I suppose that’s because it’s an exact synonym of abated, which modern english speakers will use quite commonly.
Do you mean words that only exist because they appear in an idiom but have fallen out of use elsewhere? Like “spick” in “spick and span”, or “kith” in “kith and kin”?
They’re called fossil words.
I thought it was something like a ‘locked phrase’ or ‘welded phrase’ but I can’t find anything like that. I’m 90% certain it was ‘fixed expression.’
Bound collocation? Frozen idiom?
That’s what the OP was looking for. Ignorance successfully fought! 
Um, probably.
Just saw this article: word chunking…
http://www.nytimes.com/2010/09/19/magazine/19FOB-OnLanguage-Zimmer.html?ref=onlanguage