Ein weiteres Beispiel:

housewife -->   ['haʊsˌwaɪf] Hausfrau

housewife ---> [ˈhə-zəf] Nähkästchen

Der "specific technical term" dafür ist Homographie.

Homographie steht für:

• in der Linguistik ein Paar von Wörtern gleicher Schreibweise, aber unterschiedlicher Bedeutung.

(s. Wikipedia)

Könnte Sandhi der gesuchte Begriff sein?

Thanks everyone, hm's example is the closest to what I'm talking about, I suppose. It's not about allophones, there's plenty of these, think of all the nouns and verbs where you stress the first syllable in the noun but the latter in the verb.

It's really specific to the pronunciation of the vowel, and the meaning appears to stay the same. Another one I've just thought of is can:

e.g. I don't know I can. → /'cæn/

I can help. → /cən/

Again æ → ə. 'A schwa or a full vowel sound,' just as you say, hm. The vowel is somehow reduced to a laxer form or something like that. The word I'm looking for doesn't describe the words that exhibit this property but rather the process of vowel mutation as a feature of a language.

This may be relevant:

https://en.wikipedia.org/wiki/Vowel_reduction

You yourself used the word "reduced".

Weak form/strong form hätte ich noch anzubieten.

#1 fragt nach Ausspracheunterschieden je nach Kontext, #2 bringt ein Beispiel für Ausspracheunterschiede je nach Bedeutung.

PeterK hat recht: ich hatte nicht gründlich genug gelesen. (An das Nähkästchen erinnerte ich mich aus Studententagen; dass das heute obsolet ist, mag sein.

Wer hat überhaupt noch eines?)

Weak and strong forms (vowel reduction)

Danke Jan, das ist es!

"Some monosyllabic English function words have a weak form with a reduced vowel, used when the word has no prosodic stress, and a phonemically distinct strong form with a full vowel, used when the word is stressed (and as the citation form or isolation form when a word is mentioned standing alone). In the case of many such words the strong form is also used when the word comes at the end of a sentence or phrase.

An example of such a word is the modal verb can. When appearing unstressed within a sentence and governing a verb (as in I can do it), the weak form /kən/ is used. However the strong form /kæn/ is used:

• when the word is stressed: I don't have to do it, but I can do it
• when the word is phrase-final, i.e. without a governed verb: we won't be doing it, but they can if they want
• when the word is referred to in isolation: The verb "can" is one of the English modals."