Synonyms for the word "under-coats" are various and can be used interchangeably depending on the context. One of the most common synonyms is "base layer," which refers to the layer of clothing worn closest to the skin. Other synonyms include "innerwear," "thermal wear," "long johns," and "undershirts." These terms are often used to describe clothing that provides an additional layer of insulation, particularly during colder months. In addition, the term "undercoat" can also refer to the layer of paint applied before the final coat. Synonyms for this type of "undercoat" include "primer," "basecoat," or "sealer." Overall, the variety of synonyms available for the term "under-coats" allows for flexible use, conveying different layers of meaning and context.