Matter of aptness refers to the relevance or suitability of something in a particular situation. Synonyms for this expression would include appropriateness, fitness, suitability, relevance, pertinence, and timeliness. These words convey the idea of an appropriate match between the subject and the situation it relates to. Other possible synonyms might include congruence, compatibility, harmony, and consonance, which describe the idea of a smooth fit between different elements. "Matter of aptness" can apply to many different contexts, whether it be selecting the right words for a speech, choosing the right clothes for an occasion, or picking the right tools for a job.