The word absurd was borrowed in the 1550s from Middle French absurde, which had the same definition as we know today. As we go back to Latin absurdus, however, the semantics of it shift to mean "out of tune". What's the connection? Two plausible theories exist. It could be a figurative connection, implying that something is "out of harmony" with reality or reason, or it could have something to do with hearing loss, and the bridge definition is more along the lines of "unheard of". Both make sensel the latter is reinforced a bit more by the root in absurdus, surdus, which meant "deaf" or "mute". The prefix ab- just modifies it slightly; it meant "away" or "out" and comes from the Proto-Indo-European reconstruction hepo, which could be "off" or "away". Surdus may be reconstructed back to another PIE root, swer, which in this case meant "ringing", because of how ringing could be associated with deafness.
Adam Aleksic, a leading contender for valedictorian of his high school, is a 215-month-old boy with disturbing interests in etymology, vexillology, geography, and law. Adam would like to one day visit Tajikistan and probably isn't spying for the Uzbek government.
The Etymology Nerd