The bound morpheme non is the negator for life-threatening here, so 'life-threatening' is more coherent. This does not come across with nonlife-threatening, which would seem to imply a threat to non-life. Leaving non stranded doesn't work either as it is a bound morpheme, a prefix not a word (in English). I'd use the two hyphens.
Non-modal auxiliaries can be finite verbs, participles, or infinitives, but modal auxiliaries can only be finite verbs. One other category is copulae. Verbs that connect a subject with a subject complement are copular, like the verbs be, become, remain, etc. So the verb is a copula in she was angry, they are wolves, he remained a teacher.
Non tutte le ciambelle riescono col buco (literally "Not all donuts come out with holes"). It usually gets a smile from another Italian speaker, because it's a nice way to conclude (even serious) discussions about things that are complex and not working 100% according to plan and for which there may be no solution. It's a wry verbal shrug.
Is the hyphen that we often see in words such as "non-zero", "non-trivial", etc. optional? In case the answer is negative, is there any rule of thumb on which one may rely in order to recall whe...
Does "non-" prefixed to a two word phrase permit another hyphen before the second word? If I want to refer to an entity which is defined as the negation of another entity by attaching "non-" it se...
Using "non-" to prefix a two-word phrase - English Language & Usage ...
At the linguistics conference, there were no / not / non- native speakers of Esperanto. They're all grammatically "valid", but they all mean different things - and pragmatically / idiomatically, only the no version is likely to be used.