【Spell】 ,  【shift】 ,  【tour】 ,  【trick】 ,  【turn】 ,  【stint】 ,  【bout】 ,  【go】  can mean a limited period or amount of some activity that often follows a schedule.

【Spell】 is ordinarily used in reference to very heavy or trying work which must be interrupted by a period of rest; the period may vary according to the laboriousness of the activity and the need of relief from it.

【Shift】 suggests a change in time or hours of duty and therefore a change in the workers employed; it is used especially in reference to an industrial plant which is in continuous operation, and is applied variously to the period of work or to the body of workers engaged to work during that period.

【Tour】  occurs chiefly in the phrase  【tour】 of duty ; it usually suggests a change in the character of the work and in its typical use (as of military or naval personnel) implies assignment for a definite term (as of weeks, months, or years) to a particular type of duty or to duty in a particular place.

【Trick】 , like  【spell】 , usually implies the time allotted to one for working at or as if at the helm of a ship, and it may differ little from  【shift】 as applied to a period of work.

【Turn】 in general use suggests an opportunity of a specified kind (as for work or play) or for a particular period that comes in alternation, rotation, or at more or less regular intervals.

【Stint】  (see also TASK ) implies either an assigned amount of work or an assigned amount of time in which to accomplish it. The term is used widely in reference to one’s own occupation, to the work of running a home, a farm, or a business, or to work in an industrial field especially where regular hours for a day’s work are not or cannot be easily established.

【Bout】 , which has many specific applications and is perhaps more widely employed than any of the preceding terms, in general suggests an activity or condition that is marked by a definite beginning and end in time; specifically it may refer to a fight, an attack of illness and especially of a recurrent illness, or a 【spell】 (as of drinking, of work, or of exercise), but in every case it implies a beginning or end that marks it off from what precedes and follows.

【Go】  is often not clearly defined in meaning, but it comes close to  【bout】 ,  【spell】 , and  【turn】 , in suggesting a restricted period.