Double Bass Was There Ever A Time Where The Double Bass And Contrabass Were Different Instruments?

Well, anyway, I let this thing get a bit off track. Whatever the origin of the term "double bass", there seems to be a consensus that it's always been the same thing, whether called "contrabass" or "double bass" - in other words, the lowest member of the violin family, lower than what we now call the "cello". There has been a huge amount of variation in the physical characteristics of these things, but as far as I know, the two names have always been applied to the same set of instruments.
 
there seems to be a consensus that it's always been the same thing, whether called "contrabass" or "double bass" - in other words, the lowest member of the violin family, lower than what we now call the "cello".

The important thing to bear in mind is that we use these terms as if they're nouns, but they're all adjectives and the noun is usually implied. Look at them as adjectives and this question becomes a lot simpler to answer.

I don't play a bass, I play a bass viol (or violin, I think the distinction lacks a difference anymore). I don't play a cello, I play a violoncello. The reed player plays not a bass but a bass clarinet, or rarely a contrabass clarinet, a quite different instrument another octave down — or bass saxophone, or bass flute. The brass guy's instrument used to be a bass horn, and you'll still sometimes find his part notated 'Bass,' but we normally call it a tuba (which is Latin for 'horn,' so 'bass tuba' actually makes sense).
 
It might be worth adding, that - as far as I know - only the English language have the Double Bass terminology. In all other Germanic and Roman languages it’s called a Kontrabas (Scandinavia), Kontrabaß (Germany), Contrebasse (France), Contrabajo (Spain), Contrabbasso (Italy). The ‘Double Bass’ equivalent doesn’t exist in these languages.

To me, it will always be a Contrabass, for that very reason. My personal theory is, that ‘Double Bass’ may have been a terminology that eventually got adopted; a bit like the ‘Upright Bass’ would do later on (I do not like that term, either, btw.)
 
My degree is in string bass which I always found the most accurate descriptor.

Yes, but to me that term sounds simplistic, soulless and hollow; as if devised for High School students.

To me the term Double Bass, whatever it's origins, has now settled to uniquely describe our instrument.
Just as Cello's origins describe an instrument as being smalls in in Violone-cello=Small Violone.
Cello now uniquely describes our little brother.

In English, Contrabass is often pre-fix for other instruments.
I have herd it used instead of Double Bassoon as Contrabass Bassoon.
And the very rare Contrabass singers which I saw a documentary on. Fascinating.
 
Now you opened up another can of worms. Is the double bass/contrabass actually a member of the violin family?
Yes!

Fretless: check! Bowed: check! Written into the strings section of every orchestral piece since way way back there: check!

Yes, there are some construction details borrowed more from the viols than from the smaller violins, but those are functionally driven. Flat backs - well, you ever price a baulk of tonewood thick enough to make a DB back, and compared it to one 3/16" thick? Sloping shoulders - well, you can't have it as square shouldered as a violin if you want to play in thumb position. Tuned in fourths: well, you CAN tune it in fifths and a few do, but you've either got to have hands like Bill Walton or shift with every note. So tune the thing in fourths!

It's a member of the violin family.