"pleasant to the taste," 1560s, from -some (1) + tooth in a figurative sense of "appetite, taste, liking" attested from late 14c. (compare sweet tooth, also figurative use of palate). The extended sense of "attractive" (1550s) is attested earlier. Related: Toothsomely; toothsomeness.
a toothsome blonde in a tight dress
tooth-ache
toothbrush
toothless
toothpaste
toothpick
toothsome
tootle
toots
tootsy
top
topaz