Merriam-Webster's Collegiate® Dictionary, 11th Edition
SUSTAIN
I. transitive verb see: sub-
Date: 13th century
to give support or relief to, to supply with sustenance ; nourish , keep up , prolong , to support the weight of ; prop , to buoy up ,
6. to bear up under, suffer , undergo ,
7. to support as true, legal, or just, to allow or admit as valid , to support by adequate proof ; confirm , sustainedly adverb sustainer noun
II. noun
Date: 1972
a musical effect that prolongs a note's resonance