means The probability or chance that something will happen, weighed as more or less plausible.

from Built from 'likely' plus the noun-making suffix '-hood' — the same '-hood' found in 'childhood' and 'neighborhood,' which descends from Old English 'had,' meaning a state or condition. So 'likelihood' is literally 'the condition of being likely.' 'Likely' itself comes from Old Norse 'líkligr,' related to Old English 'gelíc' ('alike, similar'), the root that also gives us 'like' — the original sense being that something has the appearance or resemblance of truth, of being probable.