Part of the reason it went to "Holy Spirit" was 'cause these days "ghost" is too much associated with something frightful, or hauntings, or even worse--Casper (friendly as he is). But both words connote wind or breath--"spirit" as in-SPIRE or ex-SPIRE. Ghost-gust (as of wind). In Hebrew, "ruach"=wind=spirit as in what God breathed into Adam to give him life, where "nephish" (sp?) is "soul" or "spirit" in that dualistic sense. "Give up the ghost" is most like more about taking and ex-piring yer last BREATH than some ectoplasmic, glowing wisp like ya see in the movies.