at \at\, prep. as. aet; akin to ohg. az, goth., os.,  icel.
   at, sw. at, dan.  l. ad.
   primarily, this word expresses the relations of presence,
   nearness in place or time, or direction toward; as, at the
   ninth hour; at the house; to aim at a mark. it is less
   definite than in or on; at the house may be in or near the
   house. from this original import are derived all the various
   uses of at. it expresses: 
   1913 webster

   1. a relation of proximity to, or of presence in or on,
      something; as, at the door; at your shop; at home; at
      school; at hand; at sea and on land.
      1913 webster

   2. the relation of some state or condition; as, at war; at
      peace; at ease; at your service; at fault; at liberty; at
      risk; at disadvantage.
      1913 webster

   3. the relation of some employment or action; occupied with;
      as, at engraving; at husbandry; at play; at work; at meat
      eating; except at puns.
      1913 webster

   4. the relation of a point or position in a series, or of
      degree, rate, or value; as, with the thermometer at
      80deg; goods sold at a cheap price; a country estimated
      at 10,000 square miles; life is short at the longest.
      1913 webster

   5. the relations of time, age, or order; as, at ten o'clock;
      at twenty-one; at once; at first.
      1913 webster

   6. the relations of source, occasion, reason, consequence, or
      effect; as, at the sight; at this news; merry at anything;
      at this declaration; at his command; to demand, require,
      receive, deserve, endure at your hands.
      1913 webster

   7. relation of direction toward an object or end; as, look at
      it; to point at one; to aim at a mark; to throw, strike,
      shoot, wink, mock, laugh at any one.
      1913 webster

   at all, at home, at large, at last, at length, at
   once, etc. see under all, home, large, last phrase
      and syn., length, once, etc.

   at it, busily or actively engaged.

   at least. see least and however.

   at one. see at one, in the vocabulary.
      1913 webster

   syn: in, at.

   usage: when reference to the interior of any place is made
          prominent in is used. it is used before the names of
          countries and cities esp. large cities; as, we live
          in america, in new york, in the south. at is commonly
          employed before names of houses, institutions,
          villages, and small places; as, milton was educated at
          christ's college; money taken in at the customhouse; i
          saw him at the jeweler's; we live at beachville. at
          may be used before the name of a city when it is
          regarded as a mere point of locality. "an english king
          was crowned at paris." --macaulay. "jean jacques
          rousseau was born at geneva, june, 28, 1712." --j.
          morley. in regard to time, we say at the hour, on the
          day, in the year; as, at 9 o'clock, on the morning of
          july 5th, in the year 1775.
          1913 webster
see also:
at all at home at large at last at length at once 
all home large last length 
once at it at least least however 
at one in at