The Collaborative International Dictionary of English v.0.48:

Assail \As*sail"\ ([a^]s*s[=a]l"), v. t. [imp. & p. p.
   Assailed (-s[=a]ld"); p. pr. & vb. n. Assailing.] [OE.
   assailen, asailen, OF. asaillir, assailler, F. assaillir; a
   (L. ad) + saillir to burst out, project, fr. L. salire to
   leap, spring; cf. L. assilire to leap or spring upon. See
   Sally.]
   1. To attack with violence, or in a vehement and hostile
      manner; to assault; to molest; as, to assail a man with
      blows; to assail a city with artillery.
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            No rude noise mine ears assailing.    --Cowper.
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            No storm can now assail
            The charm he wears within.            --Keble.
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   2. To encounter or meet purposely with the view of mastering,
      as an obstacle, difficulty, or the like.
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            The thorny wilds the woodmen fierce assail. --Pope.
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   3. To attack morally, or with a view to produce changes in
      the feelings, character, conduct, existing usages,
      institutions; to attack by words, hostile influence, etc.;
      as, to assail one with appeals, arguments, abuse,
      ridicule, and the like.
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            The papal authority . . . assailed.   --Hallam.
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            They assailed him with keen invective; they assailed
            him with still keener irony.          --Macaulay.
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   Syn: To attack; assault; invade; encounter; fall upon. See
        Attack.
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WordNet (r) 3.0 (2006):

assail
    v 1: attack someone physically or emotionally; "The mugger
         assaulted the woman"; "Nightmares assailed him regularly"
         [syn: assail, assault, set on, attack]
    2: launch an attack or assault on; begin hostilities or start
       warfare with; "Hitler attacked Poland on September 1, 1939
       and started World War II"; "Serbian forces assailed Bosnian
       towns all week" [syn: attack, assail] [ant: defend]
    3: attack in speech or writing; "The editors of the left-leaning
       paper attacked the new House Speaker" [syn: attack,
       round, assail, lash out, snipe, assault]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "assail":
   ambush, assault, attack, blister, blitz, bushwhack, castigate,
   censure, come at, come down on, crack down on, criminate,
   cry out against, cry out on, cry shame upon, descend on,
   descend upon, excoriate, fall on, fall upon, flay, fustigate,
   gang up on, go at, go for, harry, have at, hit, hit like lightning,
   implicate, impugn, incriminate, inculpate, involve, jump, land on,
   lash, lay at, lay hands on, lay into, light into, mug, pitch into,
   pounce upon, pound, roast, sail into, scarify, scathe, scorch,
   set on, set upon, skin alive, slash, strike, surprise,
   swoop down on, take the offensive, trounce, wade into