A compound verb is a combination of two or more words that function as a single complex predicate. Typically, there is a main verb and an auxiliary verb. The use of this structure varies from language to language. Compound verbs are found frequently in English, most commonly in the expression of tenses, and less often in other languages.
Compound verbs are often used to indicate the time of action in English. Most commonly, the combination of "will" followed by a verb indicates action in the future, and the present tense of the verb "to be" combined with a present participle is a form of present tense that indicates action occurring, such as "He is playing baseball." The present tense of the verb "to have" combined with the past participle of the main verb creates the present perfect tense to indicate action that has taken place in the past but might not be completed. "I have lived here for 20 years" is an example.
In the English present tense, the verb can be simple or compound, with somewhat different meanings for each structure. "I eat" is a general phrase that could mean that a person is not starving or that he or she is eating now. "I am eating" is more explicit, and "I do eat" is an emphatic way of expressing the fact that the speaker is not starving. The infinitive also forms a common compound verb construction. "I have to eat," "I want to eat" and "I am going to eat" all express different thoughts about eating.
Although English relies heavily on compound verbs to express the time that an action takes place, in Spanish, this is sometimes accomplished by the conjugation of the verb. The conditional and future in Spanish are produced this way. In some languages, such as Thai, there is no conjugation, and the time of an action is given by the present tense of the verb plus an adverb or adverbial phrase to identify when the action takes place.
A serial verb is sometimes mistaken for a compound verb. The difference lies mainly in the equality of the verbs and usually is given away by a connecting conjunction. "He up and left the table" is an example of a serial verb that has become a colloquial English idiom in which the word "up" is used as a verb.
There is some difference of opinion over the exact meaning of the phrase "compound verb." Some authorities include structures such as "He went missing" as an example of a compound verb. Others believe that "missing" is better identified as a gerundive used as a noun.
In German, the separable verbs, of which there are many, are sometimes called compound verbs. These verbs are constructed of a main verb plus a prefix that in English would take the form of a preposition. The prefix is often disengaged from the main verb, but the meaning is the same as if the parts of the "compound verb" were not separated.