1 [noncount] : a state in which someone is carefully looking for possible danger, threats, problems, etc.
▪ There were dozens of police officers standing/keeping guard along the parade route. ▪ Several soldiers were on guard [=watching and ready to respond if needed] at the gate. ▪ The soldiers were on their guard. [=they were watching and ready to respond] ▪ We need to be on guard against attack. [=we need to be alert so we are not attacked; we should be prepared to be attacked] ▪ He always has/keeps his guard up [=is careful and alert] during negotiations. ▪ She never lets down her guard. = She never lets her guard down. [=she never relaxes and stops being careful and alert] 2 a [count] : a person whose job or duty is to watch and protect someone or something
▪ There were several (armed) guards stationed at the gate. ▪ (US) a prison guard [=someone who watches prisoners to prevent their escape] — see also security guard
b [count] : a group of people (such as soldiers) who protect a person or place
▪ the palace guard ▪ Tourists gather every day to watch the changing of the guard at Buckingham Palace.
c the Guards : soldiers who protect a king or queen
▪ the Royal Horse Guards — see also color guard, honor guard, old guard, rearguard 3 [count] a : something that keeps an unwanted result or effect from happening — often + against ▪ The wound should be thoroughly cleaned as a guard against infection. — see also safeguard
b : a special part or device that protects someone or something from injury or damage
▪ The guard must be in place before operating the meat slicer. ▪ a mouth/shin guard 4 [count] a American football : either one of two players who play in positions on either side of the center
b basketball : either one of two players who usually play away from the basket and control their team's play when they are trying to score points — see also point guard 5 [count] Brit : conductor 2