Synonyms: heads-up
Definition: a warning message
Usage: he sent a heads-up to the District Attorney
Similar words: warning
Definition: a message informing of danger
Usage: a warning that still more bombs could explode
Synonyms: wide-awake, heads-up
Definition: fully alert and watchful
Usage: played heads-up ball
Similar words: alert, watchful
Definition: engaged in or accustomed to close observation
Usage: caught by a couple of alert cops; alert enough to spot the opportunity when it came; constantly alert and vigilant, like a sentinel on duty