The Collaborative International Dictionary of English v.0.48:

Frequent \Fre*quent"\, v. t. [imp. & p. p. Frequented; p. pr.
   & vb. n. Frequenting.] [L. frequentare: cf. F.
   fr['e]quenter. See Frequent, a.]
   1. To visit often; to resort to often or habitually; as, to
      frequent a tavern.
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            He frequented the court of Augustus.  --Dryden.
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   2. To make full; to fill. [Obs.]
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            With their sighs the air
            Frequenting, sent from hearts contrite. --Milton.
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The Collaborative International Dictionary of English v.0.48:

Frequent \Fre"quent\, a. [L. frequens, -entis, crowded,
   frequent, akin to farcire to stuff: cf. F. fr['e]quent. Cf.
   Farce, n.]
   1. Often to be met with; happening at short intervals; often
      repeated or occurring; as, frequent visits. "Frequent
      feudal towers." --Byron.
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   2. Addicted to any course of conduct; inclined to indulge in
      any practice; habitual; persistent.
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            He has been loud and frequent in declaring himself
            hearty for the government.            --Swift.
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   3. Full; crowded; thronged. [Obs.]
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            'T is C[ae]sar's will to have a frequent senate.
                                                  --B. Jonson.
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   4. Often or commonly reported. [Obs.]
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            'T is frequent in the city he hath subdued
            The Catti and the Daci.               --Massinger.
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WordNet (r) 3.0 (2006):

frequent
    adj 1: coming at short intervals or habitually; "a frequent
           guest"; "frequent complaints" [ant: infrequent]
    2: frequently encountered; "a frequent (or common) error is
       using the transitive verb `lay' for the intransitive `lie'";
    v 1: do one's shopping at; do business with; be a customer or
         client of [syn: patronize, patronise, shop, shop
         at, buy at, frequent, sponsor] [ant: boycott]
    2: be a regular or frequent visitor to a certain place; "She
       haunts the ballet" [syn: frequent, haunt]

Moby Thesaurus II by Grady Ward, 1.0:

62 Moby Thesaurus words for "frequent":
   affect, attend, automatic, beaten, common, constant, continual,
   continuing, continuous, countless, customary, cyclical,
   ever-recurring, everyday, familiar, frequentative, habitual,
   hackneyed, hang around, hang out, hang out at, haunt, haunting,
   incessant, infest, innumerable, iterative, many, many times,
   normal, not rare, numerous, of common occurrence, oft-repeated,
   oftentime, ordinary, overrun, patronize, periodic, persistent,
   prevalent, reappearing, recurrent, recurring, regular, reiterative,
   repeated, repetitive, resort, resort to, returning, revenant,
   routine, stereotyped, thematic, thick-coming, trite, ubiquitous,
   usual, visit, well-trodden, well-worn