贸 is a bound form (黏着语素) that cannot stand alone in modern Chinese. It carries the meaning of 'commerce, trade' and always appears in compound words — the most common being 贸易 (mào yì, trade/commerce), 经贸 (jīng mào, economy and trade), 外贸 (wài mào, foreign trade), and 商贸 (shāng mào, commerce/trade). Unlike the English word 'trade', 贸 never functions as an independent noun or verb; it must be combined with another character. When you encounter 贸 in reading, it will always be part of a fixed compound.