1 (mentally acute) [+person] espabilado; despierto He's nearly 90 now but still mentally alert
[+expression] vivo they were alert eran espabilados; tenían la mente despierta; he's a very alert baby es un bebé muy despierto
2 (vigilant) alerta; atento We all have to stay alert He had been spotted by an alert neighbour
we must stay alert hay que estar atentos
3 (aware) to be alert to sth ser consciente al tanto de algo;or
The bank is alert to the danger He said the US would be very alert to the possibility of terrorism Bringing a new pace to the musical, he was continually alert to fresh developments ...