+1 Very interesting point. I was unaware that other languages retained the "Saint" (or used similar expressions, for that matter).

Dutch has also secularised it as ongelovige Thomas (literally: disbelieving Thomas)

Then the question remains why one would object to using the expression (or look fo ran alternative). Would one then also spurn the use of Herculean or Oedipus complex (both obviously religion-based) or avoid teh use of the plethora of sayings and expressions that originate from the (King James) bible, like an eye for an eye?

@oerkelens - you should ask OP, but I don't thinks he objects to using "non secular" expressions. Why the term "Saint" didn't enter the English and probably other European languages is a point to make, I think.

@oerkelens I don't particularly object to using "doubting Thomas." My question is asked foremost out of curiosity. The question, and many of the responses (including your comment), have reminded me just what a powerful influence Christianity has had on the English language.

In German there is the "ungläubiger Thomas" as well. No reference of Saint there either. Translates to "disbelieving Thomas" like the Dutch version @gerrit mentioned.

@Helmar - interesting, it is probably a Catholic vs Protestant issue which influenced the usage of the term "Saint".

@Josh61 likely, although both are almost equally widespread in Germany but certainly the country is not as Catholic as France, Italy or Spain. It's about 30% Protestant, Catholic and irreligious each.

The french sentence sounds really weird. Where did you get it from?

@Josh61 it does! (except the ne n' which is a repetition of ne, which is probably a typo?) (I think a common sentence is Je ne crois que ce que je vois, comme Saint Thomas)

I don't think this is valid at all. Whether "Saint" is used is immaterial. The simple fact remains that Thomas is a character in the bible who insisted on seeing Jesus' injuries else he wouldn't believe he was crucified. Importantly, Thomas was rebuked as he dared to be skeptical... A secular version is still required, as it seems rather unnecessarily magical and supernatural to be using a story where a person was encouraged to believe without evidence. I would think a secular person should want to use a story where skepticism was encouraged.

@PandaWood - the origin is the same, but the fact that the term "Saint" never entered the English (and other languages) use means something. "Saint" is a special term with deep religious implications, and not using it may likely imply a "secularization" of the saying. How many people could guess the religious origin of a " doubting Thomas" compared to "doubting Saint Thomas" ?

In Czech, it's "nevěřící Tomáš" (disbelieving Thomas) as well. And we are quite a disbelieving country :).

In Russian, the phrase goes "Фома неверующий" ("Thomas the disbelieving"), no mentions of "saint".

@Edheldil the "Saint Thomas" is too many words, is the only explanation needed for that omission. It means absolutely nothing. It's like suggesting that the use of "Sir Richard Branson" instead of "Richard Branson" within a historical story "meant something". It may have simply been omitted for brevity or that it wasn't known to the story teller. Either way, it would not mean anything.

@PandaWood - Saint means nothing ? probably just to you!

@Josh61are you being deliberately naive? The "omission" of it means nothing when it's being suggested to us that it's omission is a deliberate and definite secularization

This is almost certainly due to protestantism and/or convenience, not secularization.

"Saint" is often omitted in French (Quebec).