The association of strange = foreign and strange = enemy is common enough in languages, but of course we also have stranger = guest.

The words 'guest' and 'hostile' are related, being the Germanic and Romance reflexes of PIE *ghost-, 'stranger', acquiring in Latin especially the sense 'enemy', thus a host = an army.

It is unrelated to ghost = spectre, or to host = eucharist.

It is probably related to host = one who receives you, from Latin stem hospit- (so also hospital, hospice, hotel), which is probably from hosti-pot- 'guest master', the second bit being from the root pot- 'power'. The same second part appears in Greek des-pot- 'house master'.

:-)