apt

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. liable, likely.

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.