Exodus 12:8-9 mandates that the passover sacrifice be roasted with fire (צְלִי־אֵ֔שׁ), and prohibits its consumption when raw or when boiled in water (נָ֔א וּבָשֵׁ֥ל מְבֻשָּׁ֖ל בַּמָּ֑יִם). In contrast, Deuteronomy 16:7 uses the same verb (בֹשׁל) to describe the mandated preparation method.
The definitions given in HALOT for בֹשׁל (also בָּשֵׁל) for each stem are:
- qal: grow ripe, boil
- piel: boil, cook, fry
- pual: be boiled, be cooked
- hifil: ripen1
The translations listed in the question (NIV, ESV, NET, HCSB, NRSV, NASB and KJV) are compared with all morphological inflection ignored for ease of comparison (the English lemma is given), and the Hebrew stem is listed in the first column (pardon an image file, Markdown is horrible with tabular data):
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Below is a visual representation of the senses of the verb as generally translated into English. Note that 'roast' only appears once (in 2 Chronicles 35:13, which will be addressed shortly).
The Septuagint is also notable for Deuteronomy 16:7, where it resolves contradiction by saying, "and you shall boil and roast and eat..." (καὶ ἑψήσεις καὶ ὀπτήσεις καὶ φάγῃ).
Option 1: Different senses of the same word (no contradiction)
These definitions certainly allow for some ambiguity. As pointed out by Joseph, in Numbers 11:8 — it makes more sense to 'bake' a cake than to 'boil' it. Even aside from this example, 'cook' and 'boil' are relatively ambiguous in other places as well (especially since the idea of 'boiling the flesh' over fire appears in a few passages as well, see chart).
Option 2: Rabbinical attempt to harmonize apparent conflict (contradiction)
Regardless of whether 'cook' or 'boil' is a better English translation of this term in various contexts, the question at hand is whether the original readers would have seen Deuteronomy 16:7 in conflict with Exodus 12:9. I believe the answer is yes, and 2 Chronicles 35:13 is likely an early rabbinic attempt ('the Chronicler') to resolve this contradiction by harmonizing these two passages:
וַֽיְבַשְּׁל֥וּ הַפֶּ֛סַח בָּאֵ֖שׁ כַּמִּשְׁפָּ֑ט וְהַקֳּדָשִׁ֣ים בִּשְּׁל֗וּ בַּסִּירֹ֤ות וּבַדְּוָדִים֙ וּבַצֵּ֣לָחֹ֔ות וַיָּרִ֖יצוּ לְכָל־בְּנֵ֥י הָעָֽם׃2
Literally, this passage says:
And they boiled the passover sacrifice on the fire according to the tradition and they boiled the holy offerings using pots....
It's interesting is that most English translators use 'roast' for the same verb in the first sense and 'boil' in the second. This resolves what appears to be a tautology. But what if the redundancy is an intentional attempt to harmonize Deuteronomy 16:7 with Exodus 12:9? This would only be necessary if it were perceived as a contradiction.
A source-critical approach would argue that these differences are not surprising because they simply reflect the different practices of people at different times, and a later Rabbi or scribe observed this contradiction and attempted to harmonize it with the awkward construction of boiling it with fire (effectively redefining the word). The attempt to resolve the conflict is the best evidence that an actual contradiction exists.
This instance is a well-cited example of such a harmonization.3 The presence of 'according to the tradition' (כַּמִּשְׁפָּ֑ט) is often associated with such halachic harmonizations in Chronicles. This is cited as an example of contradiction and harmonization in many introductory texts and critical commentaries (e.g. most anything published by Oxford, Cambridge, etc.).
To fully answer the question, 'בֹשׁל' should be translated consistently with Exodus 12:8-9. I recommend translating it as as 'boil' in Deuteronomy 16:7, knowing that this will place it in conflict with Exodus 12:8-9. It's the same Hebrew word.
The biggest issue for me isn't whether to use 'boil' or 'cook', but rather translating the word consistently in these passages so that the contradiction isn't hidden from the reader (when it would not have been to those reading it in its original language).
1 Ludwig Koehler et al., The Hebrew and Aramaic Lexicon of the Old Testament (Leiden; New York: E.J. Brill, 1999), 164.
2 Biblia Hebraica Stuttgartensia: SESB Version, electronic ed. (Stuttgart: German Bible Society, 2003), 2 Ch 35:13.
3 cf. Michael Fishbane, Biblical Interpretation in Ancient Israel (Oxford, UK: Oxford University Press, 1985), 135-6.