Dear friend,
Every word, irrespective of the language, has its basic literary meaning and other meanings associated with its usage. The latter one is called as connotation. That's how interchangeable usage of similar words occurs. But in law, every word or term has a certain specific meaning and hence the necessity of the definition clauses in its draft. The words thus defined in a particular law carry in their folds the positivity of the objectives of the Act carefully excluding the negativity of the mischief the Act intends to eliminate. Therefore, the differences between the words have to be understood in this back ground only.
"Employee" is a general term denoting every person employed for hire or reward under another person. Thus it presupposes the existence of a contract of employment between them that will regulate their relationship as employer and employee.So, the term has no distinction as to capacity of employment or some times even the quantum of salary or wages received. The same connotation applies equally in certain employment laws too. The best example is the definition of the term "employee" u/s 2(e) of the PG Act, 1972. Both a Managing Director of a Company and a Fitter in its factory are employees only for the purpose of gratuity under the Act. In the case of the application of the EPF Act, 1952, a distinction as to monthly salary limit is introduced.
The terms "workman" and "worker" may seemingly appear to be the same though the latter is gender-neutral. But legally, the meanings are totally different. As per section 2(s) of the ID Act, 1947, a workman can be anyone employed under a contract of employment for doing any skilled, unskilled manual, technical, clerical, operational or supervisory nature of work for hire or reward. But only the supervisory capacity of such employment is limited by the quantum of salary drawn up to a sum of Rs.10000/=pm. If we carefully analyze the definition, we can easily understand that only those employed on jobs of repetitive nature having no scope of decision making in tune with the qualitative changes in the flow of the work assigned are included in the definition without any restrictions.That's why administrative/ managerial personnel are explicitly brought out of the definition. Thus the definition of the term "workman" under the IDA, 1947 syncs with the objective of investigation, prevention and resolution of industrial disputes.
On the contrary, the purpose of the Factories Act, 1948 is regulation of conditions of work in factories including health and safety of the people employed therein, it requires a different type of definition encompassing all the people directly involved in the manufacturing process sans the cadre differences. Therefore, the definition "worker" u/s 2(l) of the FA, 1948 includes all managerial, supervisory and workmen engaged in the manufacturing operations within the factory premises.
If you look at the State Shops and Estts Acts, the term used would be "Person employed" denoting the employment being wholly and principally in connection with the business of the establishment. Of course, a managerial cadre employee who is authorised to act as the employer is exempted from the definition.
Hope I have answered to your satisfaction.