The spelling of the archaic term "hadst fling at" can be explained using the International Phonetic Alphabet (IPA). "Hadst" is pronounced as /hædst/ and means "you had". "Fling" is pronounced as /flɪŋ/ and means "to throw forcefully". "At" is pronounced as /æt/ and means "in the direction of". Therefore, the phrase "hadst fling at" means "you had thrown forcefully in the direction of". This phrase may not commonly be used today, but it has historical significance and can be found in old literature.