Pertain comes to English via Anglo-French from the Latin verb pertinēre, meaning "to reach to" or "to belong." Pertinēre, in turn, was formed by combining the prefix per- (meaning "through") and tenēre ("to hold"). Tenēre is a popular root in English words and often manifests with the -tain spelling that can be seen in pertain. Other descendants include abstain, contain, detain, maintain, obtain, retain, and sustain, to name a few of the more common ones. Not every -tain word has tenēre in its ancestry, though. Ascertain, attain, and certain are among the exceptions. And a few tenēre words don't follow the usual pattern: tenacious and tenure are two.