"juice or fluid which circulates in plants, the blood of plant life," Middle English sap, from Old English sæp, from Proto-Germanic *sapam (source also of Middle Low German, Middle Dutch, Dutch sap, Old High German saf, and, with unetymological -t, German Saft "juice"). This is reconstructed to be from PIE root *sab- "juice, fluid" (source also of Sanskrit sabar- "sap, milk, nectar," Irish sug, Russian soku "sap," Lithuanian sakas "tree-gum"). As a verb meaning "to drain the sap from," by 1725.
word-forming element meaning "lacking, cannot be, does not," from Old English -leas, from leas "free (from), devoid (of), false, feigned," from Proto-Germanic *lausaz (cognates: Dutch -loos, German -los "-less," Old Norse lauss "loose, free, vacant, dissolute," Middle Dutch los, German los "loose, free," Gothic laus "empty, vain"), from PIE root *leu- "to loosen, divide, cut apart." Related to loose and lease.
<a href="https://www.etymonline.com/word/sapless">Etymology of sapless by etymonline</a>
Harper, D. (n.d.). Etymology of sapless. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/sapless