An Etymological Dictionary of the German Language/Annotated/Saft
Saft, masculine, ‘sap, juice,’ from the equivalent Middle High German saft, usually saf, Old High German saf (genitive saffes), neuter; corresponding to Anglo-Saxon sœp, neuter, English sap, Dutch and Low German sap. Its connection with Latin sapio (Old High German sęven, sęppen, Middle High German sęben, ‘to observe’) and sapor is conceivable on account of Old Icelandic safe, ‘sap,’ provided that an Aryan root sap, sab (compare Sanscrit sadar, ‘nectar’) seems possible (on the other band, Greek ὀπός, ‘sap,’ and Old Slovenian sokŭ are not allied). The prevalent view that Anglo-Saxon sœp and Old High German saf were borrowed from Latin săpa, ‘thick must,’ is unsatisfactory.