【Fulsome】 , 【oily】 , 【unctuous】 , 【oleaginous】 , 【slick】 , 【soapy】 are comparable when they mean too obviously extravagant or ingratiating to be accepted as genuine or sincere.
【Fulsome】 stresses a surfeit of something which in proper measure is not displeasing but which in abundance is cloyingly extravagant and offensive. Typically the term is applied to praise, flattery, and compliments, with the intent to suggest that they exceed the bounds of good taste and are lacking in truth and sincerity.
【Oily】 and 【unctuous】 both suggest the smoothness and blandness of oil.
【Oily】 , as applied to persons and their utterances and acts, carries a strong implication of an offensively ingratiating quality and sometimes suggests a suavity, a benevolence, or a kindliness that is assumed as a mask for evil or dubious ends.
【Unctuous】 , on the other hand, suggests the assumption, often in hypocrisy, of the tone or manner of one who is grave, devout, or spiritual.
【Oleaginous】 is sometimes used in place of 【oily】 or 【unctuous】 when pomposity is connoted or a mocking note is desired.
【Slick】 may suggest the assumption of a smooth, ingratiating manner, but it usually stresses the speciousness of that appearance and often imputes sly wily trickiness to the person who assumes it.
【Soapy】 comes close to 【unctuous】 in its extended sense, but it carries almost no suggestion of hypocrisy: rather it connotes an unduly soft, bland, or ingratiating manner.
