1. [n]  contraceptive device consisting of a thin rubber or latex sheath worn over the penis during intercourse
2. [n]  strongbox where valuables can be kept safe
3. [n]  a ventilated or refrigerated cupboard for securing provisions from pests
4. [adj]  of an undertaking
5. [adj]  free from risk or danger; "a safe trip"; "you will be safe here"; "a safe place"; "a safe bet"
6. [adj]  in safekeeping; "your secret is safe with me"
7. [adj]  financially sound; "a good investment"; "a secure investment"

1. \Safe\, a. [Compar. {Safer}; superl. {Safest}.] [OE. sauf,
   F. sauf, fr. L. salvus, akin to salus health, welfare,
   safety. Cf. {Salute}, {Salvation}, {Sage} a plant, {Save},
   {Salvo} an exception.]
   1. Free from harm, injury, or risk; untouched or unthreatened
      by danger or injury; unharmed; unhurt; secure; whole; as,
      safe from disease; safe from storms; safe from foes. ``And
      ye dwelled safe.'' --1 Sam. xii. 11.
            They escaped all safe to land.        --Acts xxvii.
                                                  44.
            Established in a safe, unenvied throne. --Milton.
   2. Conferring safety; securing from harm; not exposing to
      danger; confining securely; to be relied upon; not
      dangerous; as, a safe harbor; a safe bridge, etc. ``The
      man of safe discretion.'' --Shak.
            The King of heaven hath doomed This place our
            dungeon, not our safe retreat.        --Milton.
   3. Incapable of doing harm; no longer dangerous; in secure
      care or custody; as, the prisoner is safe.
            But Banquo's safe? Ay, my good lord, safe in a ditch
            he bides.                             --Shak.
   {Safe hit} (Baseball), a hit which enables the batter to get
      to first base even if no error is made by the other side.
   Syn: Secure; unendangered; sure.
   

2. \Safe\, n.
   A place for keeping things in safety. Specifically:
   (a) A strong and fireproof receptacle (as a movable chest of
       steel, etc., or a closet or vault of brickwork) for
       containing money, valuable papers, or the like.
   (b) A ventilated or refrigerated chest or closet for securing
       provisions from noxious animals or insects.
   

3. \Safe\, v. t.
   To render safe; to make right. [Obs.] --Shak.
   

A safe program analysis is one which will not reach invalid conclusions about the behaviour of the program. This may involve making safe approximations to properties of parts of the program. A safe approximation is one which gives less information.

For example, strictness analysis aims to answer the question "will this function evaluate its argument"?. The two possible results are "definitely" and "don't know". A safe approximation for "definitely" is "don't know". The two possible results correspond to the two sets: "the set of all functions which evaluate their argument" and "all functions". A set can be safely approximated by another which contains it.