Substitute
Part of speech: noun
Definition: A replacement or stand-in for something that achieves a similar result or purpose. A player who is available to replace another if the need arises, and who may or may not actually do so.
Part of speech: verb
Definition: To use in place of something else, with the same function. In the phrase "substitute X for Y", to use X in place of Y. In the phrase "substitute X with/by Y", to use Y in place of X. To remove (a player) from the field of play and bring on another in his place. To serve as a replacement (for someone or something)
Example sentence: Charity is no substitute for justice withheld.
Replace
Part of speech: verb
Definition: To restore to a former place, position, condition, or the like.To refund; to repay; to restore; as, to replace a sum of money borrowed.To supply or substitute an equivalent for.To take the place of; to supply the want of; to fulfil the end or office of.To demolish a building and build a updated form of that building in its place.To place again.To put in a new or different place.
Example sentence: Conservative, n: A statesman who is enamored of existing evils, as distinguished from the Liberal who wishes to replace them with others.