To be able to last through and handle the good times as well as the bad times. (Usually in the sense of a relationship of sorts). Thick is representative of the good times, whereas thin is representative of the bad times.
Synonyms for through thick and thin
On this page, you will find 30 slang terms related to through thick and thin. Some of the top words include: good deal, bad times, 1 min man, church, field, and 25 more.