【Use】 ,  【employ】 ,  【utilize】 ,  【apply】 ,  【avail】  can all mean to deal with something so as to give it a practical value or to make it serviceable to oneself or others.

One uses a thing, or a person when regarded as a passive object, as a means or instrument to the accomplishment of a purpose or as an aid to the attainment of an end; the thing may be concrete or it may be abstract.

One employs a person or thing that is idle, inactive, or not in 【use】 , when he puts him or it to work or finds a profitable 【use】 for him or it.

Although  【use】  and  【employ】  are often interchanged, there can be a perceptible difference in meaning: wherever the idea of serving as the means or instrument is uppermost,  【use】  is likely to be preferred; wherever the idea of engaging or selecting, of keeping occupied or busy, or of turning to account is uppermost,  【employ】  is the desirable and often the necessary choice; thus, a writer uses words effectively who knows what ones he should  【employ】  in a given context; a teacher often uses his pupils as monitors when he should keep them employed in study.

One utilizes something when he finds a profitable 【use】 for it or discovers how to 【employ】 it for a practical purpose.

One applies something when he brings it into contact or into relation with something else where it will prove its usefulness or acquire practical value. This suggestion of making a connection or bringing into contact is strong in all senses of  【apply】  (see also DIRECT RESORT ); in the present sense it can not only affect the construction but can even obscure the implication of usefulness; thus, one uses a mustard plaster to relieve a chest pain, but one applies a mustard plaster to the chest.

The same implication distinguishes  【apply】  from the other words when the idea of usefulness is stressed; thus, one who knows how to  【employ】  words reveals his ability to select those words that express his exact meaning, no more and no less, but one who knows how to  【apply】 words reveals his ability to 【use】 them relevantly, that is, in reference to the things or ideas with which they are idiomatically associated.

The implication of a useful or definite end is strongest in  【apply】 when the word carries the further suggestion of relating what is general or theoretical to what is particular or concrete, for some such practical purpose as identification or clarification of a problem or invention.

One avails (oneself of ) something or someone that is at hand or is offered by using it or him to one’s own benefit or advantage.