A change in the function of a word, as for example when a noun comes to be used as a verb (without any reduction), is generally known as conversion. Other labels for this very common process are “category change” and “functional shift.” A number of nouns such as bottle, butter, chair and vacation have come to be used, through conversion, as verbs: We bottled the home-brew last night; Have you buttered the toast?; Someone has to chair the meeting; They’re vacationing in Florida. These conversions are readily accepted, but some examples, such as the noun impact being used as a verb, seem to impact some people’s sensibilities rather negatively.

The conversion process is particularly productive in Modern English, with new uses occurring frequently. The conversion can involve verbs becoming nouns, with guess, must and spy as the sources of a guess, a must and a spy. Phrasal verbs (to print out, to take over) also become nouns (a printout, a takeover). One complex verb combination (want to be) has become a new noun, as in He isn’t in the group, he’s just a wannabe.

Verbs (see through, stand up) also become adjectives, as in see-through material or a stand-up comedian. Or adjectives, as in a dirty floor, an empty room, some crazy ideas and those nasty people, can become the verbs to dirty and to empty, or the nouns a crazy and the nasty.

Some compound nouns have assumed adjectival or verbal functions, exemplified by the ball park appearing in a ball-park figure or asking someone to ball-park an estimate of the cost. Other nouns of this type are carpool, mastermind, microwave and quarterback, which are all regularly used as verbs.

It is worth noting that some words can shift substantially in meaning when they change category through conversion. The verb to doctor often has a negative sense, not normally associated with the source noun a doctor. A similar kind of reanalysis of meaning is taking place with respect to the noun total and the verb run around, which do not have negative meanings. However, after conversion, if you total (= verb) your car, and your insurance company gives you the runaround (= noun), then you will have a double sense of the negative.