Cumulus and Thunderhead

Cumulus noun - A mass or quantity that has piled up or that has been gathered over a period of time.

Thunderhead and cumulus are semantically related. In some cases you can replace term "Thunderhead" with "Cumulus", this nouns are similar.

Thunderhead noun - A rounded projecting mass of a cumulus cloud with shining edges; often appears before a thunderstorm.

Cumulus and thunderhead are semantically related. Sometimes you can use "Cumulus" instead a noun "Thunderhead".