terra firma = the sound/ solid/ firm earth

Mare Nubium = sea of clouds

Mare Tranquillitatis = sea of tranquility

Mare Foecunditatis = sea of fertility (foecund = fecund; in English, fecund means fertile)

scaraboeus -> my dictionary doesn't have that, but it's probably something about a beetle (scarab- means beetle, or of the beetle family)

impetus = attack/ assault/ vehemence

cum grano salis = with a grain of salt

pabulum = feed/ fodder/ nourishment (pabulum cogitato = food for thought)

in articulo mortis = in time of death?

verbatim -> ad verbum = word for word (ad verbum --also ad litteram--is the actual Latin for that; "verbatim" seems to be the English

Mare Tenebrarum = sea of darkness

a posteriori = from the rear

facilis descensus Averni = the easy descent into Lake Avernus, which is near Cumae, the reputed entrance to the underworld

monstrum horrendum = dreadful monster/ monstrosity/ portent

impromptus = slow (one wouldn't think that that would be the definition....)

In pace requiescat! = Rest in peace (you're right--most commonly, "Requiescat in pace.")