Today’s word is an adjective. It’s old-fashioned slang for sexually attractive. The word toothsome originally meant “pleasing to the taste or palatable.” I’m not surprised that the word toothsome has sexual connotations because hunger and sexual desire are often equated with one another.
In ye olde days a young man might say the following to an attractive young lady he wishes to court:
I do declare, Miss Mary, you are looking most toothsome this evening.
Miss Mary would then blush coquettishly and either 1. retreat, or 2. ask him to bring her another glass of rum punch.
These days a strapping young dude on the make might say this to a smokin’ hot babe with whom he wishes to hook up:
Goddamn, Mary, you look so fucking good I could eat you with a spoon.
Mary would then lean sexily against the bar and 1. say, “That’s right, honey. You can look but you can’t touch.” or 2. Ask him to buy her another Cosmopolitan.