These words refer to factors that are outstanding or crucial, or that have considerable force or effect. Significant suggests something that is outstanding because it is especially meaningful or excellent ?although no urgency or forcefulness is necessarily suggested: a significant trend in the public-opinion polls; a significant but often overlooked masterpiece of Hellenistic art. Consequential stresses that something is meaningful, cannot be overlooked or has considerable impact on succeeding events, especially of a negative nature: a consequential contribution to the theory of cultural diffusion; a consequential decision to grant the Aborigines representation in Parliament. In another context, the word can often refer merely to the possessing of wealth or status: the town’s two or three most consequential businessman.

Important , the most general of these words, is also considerably less formal than the preceding words. As its root "important " suggests, it may refer to something that is rife with meaning, but it can also suggest almost every sense that any other word here more specifically points to. In any case, the word has been weakened by over-use, especially in the superlative, referring now to anything mildly interesting, noteworthy or of value: one of the most important battles of the war; an important new talent; an important trend towards smaller families.

Momentous and vital both refer to things that are crucial or essential. Momentous stress the great and immediate impact of an event, though it also points to significant ramifications or results, like consequential , but without any suggestion that these need be undesirable: a momentous turning point in evolution; the momentous decision to drop the atom bomb on Hiroshima. Vital , in contrast to momentous , can indicate an element that is organic and essential to the well-being or functioning of the whole: a vital organ of the body; raw materials vital to the war effort. Deriving from the Latin word for life, it often means crucial or of life-and-death importance: a vital error; a vital question. It can also describe something dynamic, full of life and energy: a vital young executive; a fresh, vital work of art.

With grave and serious , the emphasis moves to something that is urgent or crucial and that promises to have an extremely undesirable outcome. Grave is the more restricted of the two, specifically suggesting something that may well have a fatal conclusion: a grave illness; a pilot in grave danger. Occasionally the word can refer more generally to something ponderous or solemn, with no suggestion of a negative outcome: addressing me with a grave manner; a grave treatise on the new science of ethology. Serious , like important , is considerably less formal and more general than the other words here. It does suggest the crucial, ponderous or solemn, like grave , but with less emphasis on urgency and even less on negative eventualities. Like important , the word has been weakened by over-use, especially in the superlative: one of the most serious flaws in his character. Categorically, the word can distinguish the sober from the pleasant, light or comic: a serious expression on his face; a serious discussion. In this use, it is milder substitute for grave ; here, neither word necessarily suggests something usually meaningful or effective.

Weighty refers to factors that are not easily disregarded: weighty considerations that militated against an immediate counter-attack. But it can refer also to a decisive preponderance or to presentations that are excessively lengthy, abstruse or solemn: weighty data that disproved the argument for spontaneous generation; a weighty treatment of the origins of Roman fertility cults.