Somebody reached this blog by searching for, “Is the word “just” a stressed syllable?”
No doubt they’re long gone, but what a question!
Stress is inherently relational: you can only identify something as stressed in comparison to something else.
When a word is monosyllabic, there is no question about where its lexical stress is located: on the only syllable there is. So in citation form, I suppose there could just about be a sense in which you could call it a stressed syllable. It’s stressed enough, I suppose, to make it utterable.
But considering citation forms isn’t the best way of going about any phonological analysis. You need to see (for which read: hear) the word in context, so that it can be considered in its relation to the surrounding words. Only then is it possible to decide whether it is stressed (in relation to the surrounding words) or not.
Syntagmatics is the way forward, folks.