Evoke boundless happiness (6)
I believe the answer is:
elicit
'evoke' is the definition.
(synonyms)
'boundless happiness' is the wordplay.
'boundless' indicates the central letters (the limits or bounds of the word are removed).
'happiness' becomes 'felicity' (synonyms).
The middle letters of 'felicity' are 'ELICIT'.
(Other definitions for elicit that I've seen before include "Worm out" , "Draw out from, invoke" , "Draw out from, meaning or response" , "Obtain" , "Draw out or bring forth" .)