The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
Appendix I
Indo-European Roots
ENTRY:
pel-2
DEFINITION:
To fold. 1. Extended o-grade form *polt-.a.fold1, from Old English fealdan,faldan, to fold; b.faltboat, from Old High German faldan, to fold; c.furbelow, from Italian falda, fold, flap, pleat; d. (i)faldstool, from Medieval Latin compound faldistolium, folding chair; (ii)fauteuil, from Old French faldestoel, faldstool. Both (i) and (ii) from Germanic compound *faldistlaz, “folding stool” (*stlaz, stool; see st-); e.–fold, from Old English -feald,-fald, -fold, from Germanic combining form *-falthaz,*-faldaz.a–e all from Germanic *falthan,*faldan.2. Combining form *-plo-.a.decuple, multiple, octuple, quadruple, quintuple, septuple, sextuple, triple, from Latin -plus, -fold (as in triplus, threefold); b.–ploid; triploblastic, from Greek -plos,-ploos, -fold (as in haploos,haplous, single, and triploos, triple). (Pokorny 3a. pel- 802.)
laz, “folding stool” (*st
-); e. –fold, from Old English -feald, -fald, -fold, from Germanic combining form *-falthaz, *-faldaz. a–e all from Germanic *falthan, *faldan. 2. Combining form *-plo-. a. decuple, multiple, octuple, quadruple, quintuple, septuple, sextuple, triple, from Latin -plus, -fold (as in triplus, threefold); b. –ploid; triploblastic, from Greek -plos, -ploos, -fold (as in haploos, haplous, single, and triploos, triple). (Pokorny 3a. pel- 802.) 
