Sustain means to support something or keep it going. If you get hungry in the mid-afternoon, you might try snacking to sustain your energy through dinner.

Beams and rafters sustain a roof — they keep it up. If you sustain a conversation over the course of hours, you keep it going during that time. If you sustain an injury, it means you are injured. If you sustain an interest in what you're studying, it means that you're just as excited about the subject after studying as you are when you began.

Definitions of sustain
  1. verb
    lengthen or extend in duration or space
    “We sustained the diplomatic negotiations as long as possible”
    synonyms: keep up, prolong
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    continue, keep, keep on, retain
    allow to remain in a place or position or maintain a property or feature
    type of:
    bear on, carry on, continue, preserve, uphold
    keep or maintain in unaltered condition; cause to remain or last
  2. verb
    supply with necessities and support
    “She alone sustained her family”
    “The money will sustain our good cause”
    synonyms: keep, maintain
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    support by being a patron of
    maintain by seeding without human intervention
    keep up with financial support
    type of:
    have, have got, hold
    have or possess, either in a concrete or an abstract sense
  3. verb
    provide with nourishment
    “We sustained ourselves on bread and water”
    synonyms: nourish, nurture
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    be able to feed
    type of:
    cater, ply, provide, supply
    give what is desired or needed, especially support, food or sustenance
  4. verb
    be the physical support of; carry the weight of
    synonyms: hold, hold up, support
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    provide with a scaffold for support
    support, secure, or raise with a block
    bear or be able to bear the weight, pressure,or responsibility of
    support on chocks
    buoy, buoy up
    keep afloat
    support on poles
    support with brackets
    support from beneath
    prop, prop up, shore, shore up
    support by placing against something solid or rigid
    support structurally
    support by bracing
    prop up with a pillow or bolster
    brace (an archer's bow) by pressing the foot against the center
  5. verb
    admit as valid
    “The court sustained the motion”
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    type of:
    acknowledge, admit
    declare to be true or admit the existence or reality or truth of
  6. verb
    establish or strengthen as with new evidence or facts
    synonyms: affirm, confirm, corroborate, substantiate, support
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    contradict, negate
    prove negative; show to be false
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    back, back up
    establish as valid or genuine
    give supporting evidence
    confirm the truth of
    demonstrate, establish, prove, shew, show
    establish the validity of something, as by an example, explanation or experiment
    support or supply with references
    prove valid; show or confirm the validity of something
    check, check off, mark, mark off, tick, tick off
    put a check mark on or near or next to
    ascertain, assure, check, control, ensure, insure, see, see to it
    be careful or certain to do something; make certain of something
    verify by consulting a source or authority
    prove oneself
    show one's ability or courage
    prove formally; demonstrate by a mathematical, formal proof
    specify the origin of
    contradict, negate
    prove negative; show to be false
    prove to be of unsound mind or demonstrate someone's incompetence
  7. verb
    undergo (as of injuries and illnesses)
    synonyms: get, have, suffer
    suffer from; be ill with
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    break down, collapse
    collapse due to fatigue, an illness, or a sudden attack
    suffer from sudden painful contraction of a muscle
    break up, collapse, crack, crack up, crock up
    suffer a nervous breakdown
    drop like flies
    rapidly collapse, die, or drop out in large numbers
    fall over, go over
    fall forward and down
    type of:
    experience, get, have, receive
    go through (mental or physical states or experiences)
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