| on the ball(expression, idiom, keen, sharp, bright) |
| on the job(expression, idiom, keen, sharp, bright) |
| on the qui vive(expression, idiom, keen, sharp, bright) |
| open-eyed(adjective, keen, alert, careful, cautious) |
| overcautious(restrained, hesitant, reserved, cautious, suspicious) |
| perceptive(adjective, sharp, bright, sensible, lively) |
| percipient(adjective, reasoning, intellectual, mental) |
| perspicacious(adjective, sound, reasonable, smart, sensible) |
| reflective(sound, reasonable, moderate, honest, sensible) |
| reserved(adjective, reasonable, sensible, restrained, modest) |
| reticent(adjective, restrained, modest, humble, hesitant) |
| sane(adjective, sound, reasonable, moderate, honest) |
| sapient(adjective, reasonable, honest, sensible, fair) |
| sharp(adjective, keen, bright, sensible, lively) |
| shrewd(adjective, careful, wise, prudent, clever) |
| slack(adjective, wary, unenthusiastic, unwilling, disinclined) |
| sober(adjective, sound, reasonable, sensible, thoughtful) |
| sound(adjective, reasonable, moderate, honest, sensible) |
| tender(adjective, understanding, kind, sympathetic, polite) |
| thinking(sound, reasonable, sensible, reasoning, intellectual) |