on one's guard

on one's guard

1. In a watchful state; alert; vigilant.

   Synonym: on the alert

   Be on your guard against pickpockets in the railway station.

   • 1944 March and April, Chas. S. Lake, “Some C.M.Es. I Have Known: VIII—Sir H. N. Gresley”, in Railway Magazine, page 74:

     One had to be on one's guard when thus confronted and, in the course of my numerous meetings with him, I had on occasion to exercise all my wits and be prepared at a moment's notice to parry a very awkward question, to which I would much rather have given a considered reply.

• androgenous