Meaning and Name Origin
Rainer \ra(i)-ner\ as a boys' name is pronounced RAY-ner. It is of Old German origin, and the meaning of Rainer is "deciding warrior". Variant of Raynor. Related surnames are occasionally used as given names. Mount Rainier is an important landmark named for a British naval officer, but the Indian name was Tacoma or Tahoma, meaning "snowy peak". Modern use of Rainier (ray-NEER) may be influenced by Prince Rainier of Monaco. Poet Rainer Maria Rilke.
Rainer is an uncommonly occurring given name for men but a very prominent surname for both adults and children (#8620 out of 88799, Top 10%). (2000 U.S. Census)
Displayed below is an analysis of the usage of the boy name Rainer and affiliated names. Ray (#733 last year) and Raymond (#264) are the prominent alternative forms of Rainer (#unlisted). Adoption of these boy names reached its most widespread during 1930-1939 and has become significantly less since, with the versions Ray and Raymond becoming less in vogue. (Top 1000 Baby Names Records, 2014)