Probably by way of French intercedent (adjective), which seems to be more commonly attested than this English adjective. Ultimately from Latin intercedens, present participle of intercedere, and possibly borrowed twice by English, with the later borrowing being a learned borrowing.
intercedent (not comparable)
Part or all of this entry has been imported from the 1913 edition of Webster’s Dictionary, which is now free of copyright and hence in the public domain. The imported definitions may be significantly out of date, and any more recent senses may be completely missing.
(See the entry for “intercedent”, in Webster’s Revised Unabridged Dictionary, Springfield, Mass.: G. & C. Merriam, 1913, →OCLC.)
intercēdent