The word 'unlikelihood' is a modern English formation built upon the core adjective 'likely,' which stems from the Old English concept of being 'similar' or 'suitable,' and thus 'probable.' The negative prefix 'un-' is attached to negate this core meaning, creating 'unlikely' to describe something not probable. Finally, the abstract noun suffix '-hood,' historically denoting a state or condition, is appended to form 'unlikelihood,' the state or quality of being improbable. This construction follows a clear Germanic pattern of creating abstract nouns to express qualities, with the literal morphemes combining logically to mean "the state of not being probable."

Structure: un (not) + likely (probable) + hood (state or condition) - un: A prefix of Germanic origin (Old English) meaning "not," used to form negatives. - likely: An adjective of Germanic origin (Old English gelīc "similar, probable") meaning "probable" or "having a high chance of happening." - hood: A noun-forming suffix of Germanic origin (Old English -hād "state, condition, rank") used to denote a state, condition, or character.