The spelling of the word "Reininger" is straightforward once you understand its pronunciation. This surname is commonly pronounced as "RYE-nin-jer" in IPA phonetic transcription. The first syllable "RYE" is pronounced as the letter "r" followed by the diphthong "ai". The second syllable "nin" is pronounced as "nin" and the last syllable "jer" is pronounced as "jer". Therefore, the correct spelling of this surname is Reininger, which reflects the correct pronunciation.