These words refer to the breaking or cutting apart of something by force. Sever is a formal term for any such action, though it often specifically suggests the cutting of a part of from a larger whole: an accident which severed his left leg; being sure to sever auxiliary shoots from a plant so that they will not take strength away from the main stem. Sunder is an even more formal word for forceful separation, but it more often pertains to breaking something into two halves or equals. The word is now rarely used except in metaphorical sense: a civil war that sundered father from son and brother from brother.

Split may suggest any forceful cutting or tearing action: splitting rails with a sharp axe; splitting his pants when he bent over. In one of its senses, however, it relates closely to cleave , since both words can refer to a voluntary separation within an entity, often into equal halves: the way cells split during mitosis; a varsity club that split up after the group’s graduation. Whereas split is informal, often extremely so, cleave is nearly as formal as the first pair and in most uses sounds archaic. Cleave has a sense of a longer cut than split , so that two large portions fall apart: The huge battle-axe cleaved through the armour and body of the knight and sank into the ground. The word can be confusing, though, since it can apply to clinging fast as well as to breaking apart: Therefore shall a man leave his father and his mother and shall cleave unto his wife (Gen. 2:24). In most uses this word, like sunder, appears as a metaphor: the ship’s prow, gaily cleaving the waves. More specifically, the word can refer to the cutting action of such an instrument as a meat cleaver: carefully cleaving the chops of the loin.