4.See corresponding entry in Unabridged fitting, meet, germane, felicitous. Apt,pertinent,relevant all refer to something suitable or fitting. Apt means to the point and particularly appropriate:an apt comment.Pertinent means pertaining to the matter in hand:a pertinent remark.Relevant means directly related to and important to the subject:a relevant opinion.
Some usage guides insist that apt followed by an infinitive can or should be used to mean only "inclined, disposed'':He is apt to ignore matters he regards as unimportant.In fact, apt is standard in all varieties of speech and writing as a synonym for likely in contexts that suggest probability without any implication of a natural disposition toward:Hostilities are apt to break out if the confrontation is not soon resolved. She is apt to arrive almost any time now.See also liable.