My intuition is always to pronounce it "too-pull", because that follows the standard rules for how to pronounce vowels in words that are of English origin (which I will explain later). However, since it is related to the Latin suffix "plus", meaning "more" (see: quintuple), I make a conscious effort to pronounce it "tuppel" as in couple.
To clarify what I mean by "of English origin", of course all of the words in English are inherited from some other language, be that Latin, Greek, Anglo-Saxon, French, etc... I am specifically referring to words of Anglo-Saxon origin, which are not recent imports into the language.
Here is my understanding on the unspoken rules (at least, they were never explicitly taught to me) for how to pronounce English words that you have never seen before. Isolated vowels are to be pronounced in their short form when followed by two sequential vowels, and their long form when followed by one consonant and one vowel. That is, "VCC" is short, and "VCV" is long. For example, "pick" is not pronounced the same as "pike", because the vowel sound in the middle differs, even though the terminal "e" in "pike" is silent. Similarly, "bite" and "bit" only differ in the vowel sound -- a terminal "VC" acts as a "VCC" (except when it doesn't, like "put" vs "putt"... I never said there weren't any exceptions). Incidentally, this is why words with terminal "VC" frequently double the consonant when adding suffixes ("beg" -> "begging", "bed" -> "bedding", "cram" -> "cramming").
An observant person would note that "tuple" in fact follows the "VCC" form. Words or word-parts that end in "le" are frequently to be pronounced as though it ends in "el". For example, take the word "apple". There is unambiguously a vowel sound that occurs between the "pp" and the "l", so it's pronounced more like "appel". In the case of "apple", there are two consonants after the "a" even if you do flip the "le" at the end, so the "a" is short regardless. But if we reverse the "le" in "tuple", we get "tupel", which does follow the "VCV" order, so it seems like it should be pronounced "too-pull". However, we typically follow different pronunciation rules for words of foreign origin, and since "tuple" is of Latin origin, we pronounce it "tuppel". Compare the pronunciation of "avi" in "behavior" (Anglo-Saxon) to "pavilion" (Latin).
I am not a linguist in any sense, and so this is all my amateur reasoning about how English words are pronounced. When looking for Latin examples, I definitely ran into more exceptions than not, so take this all with a grain of salt.
To clarify what I mean by "of English origin", of course all of the words in English are inherited from some other language, be that Latin, Greek, Anglo-Saxon, French, etc... I am specifically referring to words of Anglo-Saxon origin, which are not recent imports into the language.
Here is my understanding on the unspoken rules (at least, they were never explicitly taught to me) for how to pronounce English words that you have never seen before. Isolated vowels are to be pronounced in their short form when followed by two sequential vowels, and their long form when followed by one consonant and one vowel. That is, "VCC" is short, and "VCV" is long. For example, "pick" is not pronounced the same as "pike", because the vowel sound in the middle differs, even though the terminal "e" in "pike" is silent. Similarly, "bite" and "bit" only differ in the vowel sound -- a terminal "VC" acts as a "VCC" (except when it doesn't, like "put" vs "putt"... I never said there weren't any exceptions). Incidentally, this is why words with terminal "VC" frequently double the consonant when adding suffixes ("beg" -> "begging", "bed" -> "bedding", "cram" -> "cramming").
An observant person would note that "tuple" in fact follows the "VCC" form. Words or word-parts that end in "le" are frequently to be pronounced as though it ends in "el". For example, take the word "apple". There is unambiguously a vowel sound that occurs between the "pp" and the "l", so it's pronounced more like "appel". In the case of "apple", there are two consonants after the "a" even if you do flip the "le" at the end, so the "a" is short regardless. But if we reverse the "le" in "tuple", we get "tupel", which does follow the "VCV" order, so it seems like it should be pronounced "too-pull". However, we typically follow different pronunciation rules for words of foreign origin, and since "tuple" is of Latin origin, we pronounce it "tuppel". Compare the pronunciation of "avi" in "behavior" (Anglo-Saxon) to "pavilion" (Latin).
I am not a linguist in any sense, and so this is all my amateur reasoning about how English words are pronounced. When looking for Latin examples, I definitely ran into more exceptions than not, so take this all with a grain of salt.