समास शब्द-रचना की ऐसी प्रक्रिया है जिसमें अर्थ की दृष्टि से परस्पर भिन्न तथा स्वतंत्र अर्थ रखने वाले दो या दो से अधिक शब्द मिलकर किसी अन्य स्वतंत्र शब्द की रचना करते हैं।

In linguistics, a compound is a lexeme that consists of more than one stem. Compounding, composition or nominal composition is the process of word formation that creates compound lexemes. Compounding occurs when two or more words or signs are joined to make a longer word or sign. Consequently, a compound is a unit composed of more than one stem, forming words or signs. If the joining of the words or signs is orthographically represented with a hyphen, the result is a hyphenated compound. If they are joined without an intervening space, it is a closed compound. If they are joined with a space, then the result – at least in English – may be an open compound.