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: In truth, politeness is artificial good humor, it covers the natural want of it, and ends by rendering habitual a substitute nearly equivalent to the real virtue.
Reserve
Part of speech: verb
Definition: To keep back; to retain.To keep in store for future or special use.To book in advance; to make a reservation.To serve again (e.g. a tennis ball).
Part of speech: noun
Definition: The act of reserving, or keeping back; reservation; exception.That which is reserved, or kept back, as for future use.A natural resource known to exist but not currently exploited.Restraint of freedom in words or actions; backwardness; caution in personal behavior.A tract of land reserved, or set apart, for a particular purpose; as, the Connecticut Reserve in Ohio, originally set apart for the school fund of Connecticut; the Clergy Reserves in Canada, for the support of the clergy.A tract of land set apart for the use of an Aboriginal group. (Compare US .)A body of troops kept in the rear of an army drawn up for battle, reserved to support the other lines as occasion may require; a force or body of troops kept for an exigency.Funds kept on hand to meet planned or unplanned financial requirements.A member of a team who does not participate from the start of the game, but can be used to replace tired or injured team-mates.
Example sentence: If money is your hope for independence you will never have it. The only real security that a man will have in this world is a reserve of knowledge, experience, and ability.