Wordnet 3.0
NOUN (1)
1.
someone who helps people (especially children) at a traffic crossing;
The Collaborative International Dictionary of English v.0.48:
crossing guard \cross"ing guard`\, n.
a person who stands at a street crossing to assist children
to cross the street safely; -- usually used near schools
during the times that children are entering or leaving the
school.
Note: Crossing guards may be employed by a municipality as
auxiliary police officers, or may be unpaid volunteers.
Some wear uniforms, others do not. They are commonly
older citizens who are retired or not employed
full-time at other tasks. At some schools, older
students from the school are trained to perform the
function of crossing guards.
[PJC]
WordNet (r) 3.0 (2006):
crossing guard
n 1: someone who helps people (especially children) at a traffic
crossing