There are many variants of "yes" and "no" in English. Two such spoken forms are transcribed into writing as "uh-huh" or "mm-hmm" ("yes", with a rise in pitch on the second syllable) and "uh-uh" or "mm-mm" ("no", with a fall in pitch on the second syllable). Their sounds are a nasal or non-nasal sound interrupted by a voiceless breathy interval for "yes", and by a glottal stop for "no". These forms are particularly useful for speakers who are at a given time unable to articulate the actual words "yes" and "no".
The word "aye" is a frequent synonym for "yes", particularly in Scotland, Ireland, and Northern England, although not always officially acknowledged as such. In December 1993, a witness in a Scottish court who had answered "aye" to confirm he was the person summoned was told by the Sheriff that he must answer either "yes" or "no". When his name was read again and he was asked to confirm it, he answered "aye" again, and was imprisoned for 90 minutes for contempt of court. On his release he said, "I genuinely thought I was answering him."
Both words are derived from adverbs in Old English. "Yes" is derived from a compound of an Old English adverb, "yea", which means "surely", and "so", and is thus "surely so", while "no" comes from an Old English adverb that means "never".