Complete the puzzle with 'er' sound words.

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Across
  1. 3. any of the flat appendages growing from a bird's skin and forming its plumage
  2. 6. a flowerless plant which has feathery or leafy fronds and reproduces by spores released from the undersides of the fronds.
  3. 7. a mythical sea creature with the head and trunk of a woman and the tail of a fish
  4. 8. a person exercising government or dominion
Down
  1. 1. a musical performance given in public, typically by several performers or of several compositions.
  2. 2. a written, typed, or printed communication, sent in an envelope by post
  3. 4. a piece of soft rubber or plastic used to rub out something written.
  4. 5. a group of elephants