Definition from Wiktionary, the free dictionary
- (grammar) A verb that links a subject to a complement that refers to the subject.
- That soup smells delicious.
- He was soaked to the skin.
- Your proposal sounds good to me.
Usage notes 
- Complements that follow copular verbs are typically adjectives or participles.
- The most important copula verbs are to be and to become.
- Other copular verbs, which usually have the sense of to be or to become: appear, feel, get, go, keep, grow, lie, look, prove, remain, resemble, run, seem, smell, sound, stay, taste, turn