1) An added part 2) Continuance 3) Continuation 4) French word used in English 5) Lengthening 6) Perpetuation 7) Protraction 8) The state of being prolonged 1) Continuance 2) Continuation 3) Lengthening 4) Lengthiness 5) Perpetuation 6) Protraction 
In music theory, prolongation is the process in tonal music through which a pitch, interval, or consonant triad is able to govern spans of music when not physically sounding. It is a central principle in the music-analytic methodology of Schenkerian analysis, conceived by Austrian theorist Heinrich Schenker. Prolongation can be thought of as a way...
• (n.) That which forms an additional length. • (n.) The act of lengthening in space or in time; extension; protraction.
Pro`lon·ga'tion noun [ French prolongation .] 1. The act of lengthening in space or in time; extension; protraction. Bacon. 2. That which forms an additional length. 
[n] - the act of prolonging something
prolongation 1. The consequence of being lengthened in duration. 2. The amount or degree or range to which something extends. 3. A prolonged or extended form. 4. To lengthen in extent, scope, or range. 5. An added part.
protraction noun the consequence of being lengthened in durationprotraction noun the act of prolonging something; `there was an indefinite prolongation of the peace talks`
the act of prolonging: the prolongation of a line. · the state of being prolonged. · a prolonged or extended form. · an added part.