| Not habitually or commonly occurring |
UNUSUAL |
| Numbers of people or things classed together |
GROUPS |
| Once ... a time |
UPON |
| Protective structures to prevent beaches washing away |
BULWARKS |
| Reflection of sound wave |
ECHO |
| Relative heaviness |
WEIGHT |
| Set of interrelated parts |
SYSTEM |
| Small migratory birds |
SWALLOWS |
| The basis for belief or disbelief |
EVIDENCE |
| The king of rock 'n roll |
PRESLEY |
| The strange ringtone is gas |
NITROGEN |
| These present times |
NOWADAYS |
| They're very seldom seen |
RARITIES |
| Thoughtless, inattentive |
CARELESS |
| Toy spool that's reeled up and down on a string |
YOYO |
| Uncover, find out |
DISCOVER |