Substitute, 1. One who stands in another's place 2. A person named in a will as heir to an estate after the estate has been held and then passed on by another specified person, Black's Law Dictionary, 7th Edn., p. 1443.
Mean 'to put in the place of another person or thing' or 'to exchange', Black's Law Dictionary, 5th Edn., p. 1281.
Means 'to serve or cause to serve in place of another person or thing; to replace with: or 'a person or thing that serves in place of another, such as a player in a game who take the place of an injured colleague' (Collins English Dictionary).
Means the replacement of one by another, which might be equal to it, but differently expressed, N.N. Chakravarty v. State of Assam, AIR 1960 Assam 11; I.C. Sharma v. Union of India, (1992) 21 ATC 63; Vijayalakshmi Rice Mills; New Contractors Company v. State of Andhra Pradesh, 1976 UJ (SC) 367.
Substitute, ordinarily would mean 'to put (one) in place of another; or 'to replace', Government of India v. Indian Tobacco Assn., (2005) 7 SCC 396.