The Collaborative International Dictionary of English v.0.48:

Strain \Strain\, v. t. [imp. & p. p. Strained; p. pr. & vb. n.
   Straining.] [OF. estraindre, estreindre, F. ['e]treindre,
   L. stringere to draw or bind tight; probably akin to Gr. ? a
   halter, ? that which is squeezwd out, a drop, or perhaps to
   E. strike. Cf. Strangle, Strike, Constrain, District,
   Strait, a. Stress, Strict, Stringent.]
   1. To draw with force; to extend with great effort; to
      stretch; as, to strain a rope; to strain the shrouds of a
      ship; to strain the cords of a musical instrument. "To
      strain his fetters with a stricter care." --Dryden.
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   2. (Mech.) To act upon, in any way, so as to cause change of
      form or volume, as forces on a beam to bend it.
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   3. To exert to the utmost; to ply vigorously.
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            He sweats,
            Strains his young nerves.             --Shak.
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            They strain their warbling throats
            To welcome in the spring.             --Dryden.
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   4. To stretch beyond its proper limit; to do violence to, in
      the matter of intent or meaning; as, to strain the law in
      order to convict an accused person.
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            There can be no other meaning in this expression,
            however some may pretend to strain it. --Swift.
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   5. To injure by drawing, stretching, or the exertion of
      force; as, the gale strained the timbers of the ship.
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   6. To injure in the muscles or joints by causing to make too
      strong an effort; to harm by overexertion; to sprain; as,
      to strain a horse by overloading; to strain the wrist; to
      strain a muscle.
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            Prudes decayed about may track,
            Strain their necks with looking back. --Swift.
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   7. To squeeze; to press closely.
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            Evander with a close embrace
            Strained his departing friend.        --Dryden.
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   8. To make uneasy or unnatural; to produce with apparent
      effort; to force; to constrain.
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            He talks and plays with Fatima, but his mirth
            Is forced and strained.               --Denham.
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            The quality of mercy is not strained. --Shak.
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   9. To urge with importunity; to press; as, to strain a
      petition or invitation.
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            Note, if your lady strain his entertainment. --Shak.
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   10. To press, or cause to pass, through a strainer, as
       through a screen, a cloth, or some porous substance; to
       purify, or separate from extraneous or solid matter, by
       filtration; to filter; as, to strain milk through cloth.
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   To strain a point, to make a special effort; especially, to
      do a degree of violence to some principle or to one's own
      feelings.

   To strain courtesy, to go beyond what courtesy requires; to
      insist somewhat too much upon the precedence of others; --
      often used ironically. --Shak.
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The Collaborative International Dictionary of English v.0.48:

Straining \Strain"ing\,
   a. & n. from Strain.
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   Straining piece (Arch.), a short piece of timber in a
      truss, used to maintain the ends of struts or rafters, and
      keep them from slipping. See Illust. of Queen-post.
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WordNet (r) 3.0 (2006):

straining
    adj 1: taxing to the utmost; testing powers of endurance; "his
           final, straining burst of speed"; "a strenuous task";
           "your willingness after these six arduous days to remain
           here"- F.D.Roosevelt [syn: arduous, straining,
           strenuous]
    n 1: an intense or violent exertion [syn: strain, straining]
    2: the act of distorting something so it seems to mean something
       it was not intended to mean [syn: distortion,
       overrefinement, straining, torture, twisting]

Moby Thesaurus II by Grady Ward, 1.0:

135 Moby Thesaurus words for "straining":
   bloat, bloating, bolting, breaking point, cautious, clarification,
   colature, coloring, confabulation, corruption, demurring,
   destructive distillation, diffident, distension, distillation,
   distortion, draining, drudging, edulcoration, effusion, elution,
   elutriation, equivocation, essentialization, exaggeration,
   excretion, exfiltration, exhausting, extraction, extravasation,
   extreme tension, exudation, false coloring, false swearing,
   falsification, falsifying, faltering, fatiguesome, fatiguing,
   filtering, filtration, grinding, grubbing, grueling, hardworking,
   haul, heave, hesitant, hesitating, inflation, jibbing, killing,
   laboring, leaching, lixiviation, miscoloring, misconstruction,
   misdirection, misinterpretation, misrepresentation, misstatement,
   misuse, ooze, oozing, overdistension, overdrawing, overexertion,
   overexpansion, overextension, overstrain, overstraining,
   overstress, overstretching, overtaxing, pegging, percolating,
   percolation, perjury, perversion, plodding, plugging,
   prevarication, pull, punishing, purification, rack, refinement,
   riddling, screening, scrupling, seep, seepage, separation,
   shilly-shallying, sieving, sifting, slanting, slaving, slogging,
   snapping point, spiritualization, sticking, stickling, strain,
   stress, stress and strain, stressful, stressfulness, stretch,
   stretching, striving, struggling, sublimation, sweating, swelling,
   taxing, tension, tentative, timid, tiresome, tiring, toiling,
   toilsome, torturing, transudation, trying, tug, weariful, wearing,
   wearisome, wearying, weep, weeping, winnowing, working