To a young beginner, a mere plaything (3)
I believe the answer is:
toy
'a mere plaything' is the definition.
'toy' can be an answer for 'plaything' ('toy' can be a synonym of 'plaything'). I'm not certain of the 'a mere' bit.
'to a young beginner' is the wordplay.
'beginner' indicates taking the first letters.
The first letter of 'young' is 'y'.
'to'+'y'='TOY'
Can you help me to learn more?
(Other definitions for toy that I've seen before include "Small breed" , "Miniature (dog)" , "Teddy or Dolly" , "Trifle with plaything?" , "A child's plaything" .)