Technically a giant monster (like Gojira) is a daikaiju.
I have several japanese terms listed on my web page: http://incolor.inetnebr.com/stuart/henshin/terms.htm
aku - evil
akuma - devil or demon
kaibutsu - creature of abnormal form, wicked creature, monster
kaijin - mysterious person (used in Tokusatsu particularly Kamen Rider to refer to monsters)
kaiju - mysterious creature, goblin, monster
yokai- evil spirit or ghost