What is an "apt comparison"? 

An apt comparison refers to a sensible comparison. This comparison compares two different objects but uses appropriate way of comparing the two. Apt is suitable for circumstances purpose. Apt came from the Latin word Aptus which means fitting, or suitable. Thus, apt comparison is like comparing to object or matter that is completely different but appears like they are likely the same or appropriate.
Adverb of apt => aptly
noun of apt => aptness
Synonyms of apt:
=> liable
=> adaptable
=> relevant
=> likely
=> particularly appropriate.