The spelling of the word "subanal" can be explained using the IPA phonetic transcription. The first syllable "sub" is pronounced as /sʌb/ which means "under" or "below". The second syllable "anal" is pronounced as /eɪnəl/ which is related to the anus or rectum. Therefore, the word "subanal" refers to something that is situated beneath or near the anus. This word can be useful in medical contexts when discussing the location of a certain condition or procedure.
Below the anus.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.