The American Heritage Dictionary, 4th Ed.(AHD4), dispatches the word with one line:

        conj. For the reason that; since.

but I have met more interesting usages recently.

One is in the very dictionary itself. The first meaning of the word forlorn, 

AHD4 states, is "appearing sad or lonely because deserted or abandoned."

Apple Inc.'s dictionary app on my laptop still thinks 'because' is a

conjunction but adds helpfully

    [informal] used to introduce a word or phrase that stands for a clause

    expressing an explanation or reason: there's probably somebody out there who

    would argue the point because internet | making a bag of popcorn with hot

    sauce for lunch because hungry.

The second is when a sentence simply ends with 'because.' My friend Monica said

"My son came [from Australia] for Christmas but he couldn't stay in my apartment

because." the other day when we chatted over the phone and explained that it

implied reasons unnecessary to mention (Covid here).

I found a thread on english.stackexchange.com, under the title "Ending a

sentence with 'because [noun]'" which started eight years ago. The top answers

say that the word is a preposition in modern grammar, and

    The form "because [noun]" allows the fuller statement giving the reasoning

    to be deduced, with the implication that there isn't really any reasoning -

    much as the sentence is jumping from because to an object, so too is the

    thinking of the speaker or those they are talking about. This is all the

    more so with the common form "because reasons" where there isn't any attempt

    to even state such an object.

AHD4 might have neglected these usages because its age. But there is no excuse

when it practices what it doesn't explain.

[To my disappointment, neither Michael Swan's "Practical English Usage" nor

Theodore Bernstein's "The Careful Writer" discusses these usages.]