The Collaborative International Dictionary of English v.0.48:

Precious \Pre"cious\, a. [OF. precious, precius, precios, F.
   pr['e]cieux, L. pretiosus, fr. pretium price, worth, value.
   See Price.]
   1. Of great price; costly; as, a precious stone. "The
      precious bane." --Milton.
      [1913 Webster]

   2. Of great value or worth; very valuable; highly esteemed;
      dear; beloved; as, precious recollections.
      [1913 Webster]

            She is more precious than rules.      --Prov. iii.
                                                  15.
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            Many things which are most precious are neglected
            only because the value of them lieth hid. --Hooker.
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   Note: Also used ironically; as, a precious rascal.
         [1913 Webster]

   3. Particular; fastidious; overnice; overrefined. Cf.
      Pr['e]cieuse, Preciosity.
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            Lest that precious folk be with me wroth. --Chaucer.
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            Elaborate embroidery of precious language.
                                                  --Saintsbury.
      [Webster 1913 Suppl.]

   Precious metals, the uncommon and highly valuable metals,
      esp. gold and silver.

   Precious stones, gems; jewels.
      [1913 Webster]

WordNet (r) 3.0 (2006):

precious
    adv 1: extremely; "there is precious little time left" [syn:
           precious, preciously]
    adj 1: characterized by feeling or showing fond affection for;
           "a cherished friend"; "children are precious"; "a
           treasured heirloom"; "so good to feel wanted" [syn:
           cherished, precious, treasured, wanted]
    2: of high worth or cost; "diamonds, sapphires, rubies, and
       emeralds are precious stones"
    3: held in great esteem for admirable qualities especially of an
       intrinsic nature; "a valued friend"; "precious memories"
       [syn: valued, precious]
    4: obviously contrived to charm; "an insufferably precious
       performance"; "a child with intolerably cute mannerisms"
       [syn: cute, precious]

Moby Thesaurus II by Grady Ward, 1.0:

173 Moby Thesaurus words for "precious":
   Gongoresque, Gongoristic, Marinistic, absolute, admired, adored,
   affected, alembicated, angel, arrant, artful, artificial, babe,
   baby, baby-doll, beloved, beyond price, buttercup, cherished,
   cherub, chichi, chick, chickabiddy, choice, choosy, classical,
   complete, consummate, costly, crass, darling, dear, dearly beloved,
   deary, decided, definitive, doll, downright, duck, duckling,
   effete, egregious, elaborate, elaborated, elegant, esteemed,
   euphemistic, euphuistic, exact, expensive, exquisite, fastidious,
   favorite, finicky, flagrant, formalistic, fussy, glaring, golden,
   good as gold, goody good-good, goody-goody, gross, hallowed,
   held dear, high-priced, hon, honey, honey bunch, honey child,
   hyperelegant, idolized, inestimable, intolerable, invaluable,
   irreplaceable, la-di-da, lamb, lambkin, love, loved, lover,
   mannered, methodical, meticulous, mincing, namby-pamby, nice,
   of great price, orderly, ostentatious, out-and-out, outright,
   overdone, overelaborate, overelegant, overnice, overprecise,
   overrefined, particular, pedantic, perfect, persnickety, pet,
   petkins, picky, popular, positive, precieuse, precieux,
   precious heart, precise, precisian, precisianistic, precisionist,
   precisionistic, pretentious, priceless, pricey, prized, profound,
   pronounced, proper, punctilious, puristic, rank, rare, recherche,
   regular, revered, rich, scrupulous, shattering, shocking, showy,
   simpering, snookums, sophisticated, squeamish, stark,
   stark-staring, studied, sugar, superlative, surpassing, sweet,
   sweetheart, sweetie, sweetkins, sweets, the veriest, thorough,
   thoroughgoing, total, treasured, unbearable, unconscionable,
   undeniable, unequivocal, unmitigated, unnatural, unqualified,
   unrelieved, unspoiled, utter, valuable, valued, venerable,
   venerated, well-beloved, well-liked, white-haired, worthy