the word.. 'selah' crops up now and then. it apparently comes from the book of psalms attributed to king david, and usually taken to mean a break in prayer. a pause.. like an orchestral directive ..
however.. i believe that this entirely neglects the idea that it maybe derived from the same source as the arabic root.. ʂlw ( صلوات. صلاة).. which has the basic meaning of blessing or prayer.. the meaning of prayer comes through loud and clear in aramaic as well ( צלו–צלותא.) i suggest it could belong to a substratum language common in the region.
though i am not sure about the statistics of interchange between the two sibilants, it is not unusual. there was much variation among the various semitic languages/dialects in sibilants.
the word is in no way obscure or rare in arabic, where it is the word for ritual prayer as well as blessing or grace..
in english (selah) it is spelled with a final 'h'. this is not strictly correct. while it is written in hebrew (סלה )with a final he, this was not a consonant: it is the symbol for a final vowel. if it were a consonant, there would be a diacritic point in the letter in the massoretic text: there is none. it is further indication that it maybe related to the root ʂlw. which makes perfect sense to me.
the spelling without the final h could become recognised in english, but honestly it doesnt make a lot of difference .... its the thought that counts. selah.