Obvious chess opening with king in play (5)
I believe the answer is:
clear
'obvious' is the definition.
(similar in meaning)
'chess opening with king in play' is the wordplay.
'opening' indicates taking the first letters.
'with' says to put letters next to each other.
'king in play' becomes 'Lear' (Shakespeare's King Lear).
The first letter of 'chess' is 'c'.
'c'+'lear'='CLEAR'
(Other definitions for clear that I've seen before include "Unimpeded" , "Jump over without contact" , "Make a profit - brighten up" , "Transparent or cloudless" , "With no jams" .)