The Collaborative International Dictionary of English v.0.48:

Precaution \Pre*cau"tion\, v. t. [Cf. F. pr['e]cautionner.]
   1. To warn or caution beforehand. --Locke.
      [1913 Webster]

   2. To take precaution against. [R.] --Dryden.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Precaution \Pre*cau"tion\, n. [F. pr['e]cation, L. praecautio,
   fr. praecavere, praecautum, to guard against beforehand; prae
   before + cavere be on one's guard. See Pre-, and
   Caution.]
   1. Previous caution or care; caution previously employed to
      prevent mischief or secure good; as, his life was saved by
      precaution.
      [1913 Webster]

            They [ancient philosophers] treasured up their
            supposed discoveries with miserable precaution. --J.
                                                  H. Newman.
      [1913 Webster]

   2. A measure taken beforehand to ward off evil or secure good
      or success; a precautionary act; as, to take precautions
      against accident.
      [1913 Webster]

WordNet (r) 3.0 (2006):

precaution
    n 1: a precautionary measure warding off impending danger or
         damage or injury etc.; "he put an ice pack on the injury as
         a precaution"; "an insurance policy is a good safeguard";
         "we let our guard down" [syn: precaution, safeguard,
         guard]
    2: the trait of practicing caution in advance
    3: judiciousness in avoiding harm or danger; "he exercised
       caution in opening the door"; "he handled the vase with care"
       [syn: caution, precaution, care, forethought]