1878, "without annoyance," from fret (n.) (see fret (v.)) + -less. By 1962 as "without frets" (of a banjo, guitar, etc.), from fret (n.2).
Entries linking to fretless
fret v.
Old English fretan "devour, feed upon, consume," from Proto-Germanic compound *fra-etan "to eat up," from *fra- "completely" (from PIE root *per- (1) "forward," hence "through") + *etan "to eat" (from PIE root *ed- "to eat"). Cognates include Dutch vreten, Old High German frezzan, German fressen, Gothic fraitan.
Used of monsters and Vikings; in Middle English used of animals' eating. Notion of "wear away by rubbing or scraping" (c. 1200) might have come to this word by sound-association with Anglo-French forms of Old French froter "to rub, wipe; beat, thrash," which is from Latin fricare "to rub" (see friction). Figurative use is from c. 1200, of emotions, sins, vices, etc., "to worry, consume, vex" someone or someone's heart or mind, from either the "eating" or the "rubbing" sense. Intransitive sense "be worried, vex oneself" is by 1550s. Modern German still distinguishes essen for humans and fressen for animals. Related: Fretted; fretting. As a noun, early 15c., "a gnawing," also "the wearing effect" of awareness of wrongdoing, fear, etc.
-less
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.
fret n.2
"ridge on the fingerboard of a guitar," c. 1500, of unknown origin, possibly from another sense of Old French frete "ring, ferule." Compare Middle English fret "a tie or lace" (early 14c.), freten (v.) "to bind, fasten" (mid-14c.).