Are yams and sweet potatoes the same?
Old English gellan (Mercian), giellan (West Saxon), class III strong verb (past tense geal, past participle gollen), from Proto-Germanic *gelnanan (cf. Old Norse gjalla "to resound," Middle Dutch ghellen, Dutch gillen, Old High German gellan, German gellen "to yell"), extended form of root of Old English galan "to sing" (source of the -gale in nightingale); from PIE *ghel- "to cry out, shout, sing." Related: Yelled; yelling.
late 14c., originally in Scottish, from yell (v.).