Idle on vacation, library binds all the letters (4)
I believe the answer is:
lazy
'idle' is the definition.
(similar in meaning)
'on vacation library binds all the letters' is the wordplay.
'on vacation' says to hollow out the word (remove centre letters).
'binds' means one lot of letters goes inside another.
'all the letters' becomes 'az' (I've seen this in other clues).
'library' with its middle removed is 'ly'.
'ly' placed around 'az' is 'LAZY'.
(Other definitions for lazy that I've seen before include "Work-shy" , "Disinclined to work" , "avoiding work" , "Averse to exertion" , "Shiftless" .)