My understanding is that both “Spirit” and “Ghost” are, according to strict dictionary definitions, reasonable translations of either the German “Geist” or the Latin “Spiritus”, for example
zeitgeist is commonly rendered “spirit of the time” (not “ghost of the time”). In English these days “ghost” has much more of a connotation of spooky haunted houses and Casper the Friendly Ghost and the disembodied spirits of dead people doomed to roam the earth and moan ominously and scare people. So for many of us moderns, “Holy Spirit” sounds more appropriate for God.