"For" with the meaning of "because"

I think this depends on your definition of "acceptable". "For" meaning "because" sounds literary or poetic or slightly dated. But I think it's certainly possible to use it in appropriate contexts:

for: mainly literary because

She began to grow nervous, for he had promised to meet her at dawn.

(Macmillan English Dictionary)

In colloquial speech it would probably sound out of place. But then again context is king.

This question pulls mind my interpretation of the etymology of "because" and it's ties to modern Spanish "por la causa" directly "for the sake" with the obvious shared root "causa" meaning cause or reason. combined in the Middle English phrase "by cause."

But, to be direct with an answer and give a source: for (prep.) Old English for "before, in the sight of, in the presence of; as far as; during, before; on account of, for the sake of; in place of, instead of," from Proto-Germanic *fur "before; in" (cognates: Old Saxon furi "before," Old Frisian for, Middle Dutch vore, Dutch voor "for, before;" German für "for;" Danish for "for," før "before;" Gothic faur "for," faura "before"), from PIE *pr- (see fore (adv.)).

From late Old English as "in favor of." For and fore differentiated gradually in Middle English. For alone as a conjunction, "because, since, for the reason that; in order that" is from late Old English, probably a shortening of common Old English phrases such as for þon þy "therefore," literally "for the (reason) that."

http://www.etymonline.com/index.php?term=for&allowed_in_frame=0