The name Rainer is a boy's name of German origin meaning "wise army". Rainer and is often added to lists like Baby Names That Mean Wise and discussed in our forums with posts like "Favourite Names in the last signature".
From the experts:
Rainer is one of those baby names that is still under-the-radar but has been quietly gaining traction: The number of boys who've received the name has doubled in the past decade, to just under 50. Part nature name and part traditional German name for boys, Rainer can claim a place among the two-syllable r-ending baby names so fashionable for boys today.