a short trip or outing to some place, usually for a special purpose and with the intention of a prompt return: a pleasure excursion; a scientific excursion.
2.
a trip on a train, ship, etc., at a reduced rate: weekend excursions to mountain resorts.
3.
the group of persons making such a journey: an excursion of tourists.
4.
a deviation or digression: excursions into futile philosophizing.
5.
Physics. the displacement of a body or a point from a mean position or neutral value, as in an oscillation.
1570s, "a deviation in argument," from L. excursionem (nom. excursio) "a running forth, excursion," from excursum, pp. of excurrere "run out," from ex- "out" + currere "to run" (see current). Sense of "journey" recorded in English by 1660s.