Extremely cheerful and always bright (6)
I believe the answer is:
clever
'bright' is the definition.
(bright can mean clever or intelligent)
'extremely cheerful and always' is the wordplay.
'extremely' means to remove the middle letters (only the extremes of the word are used).
'and' says to put letters next to each other.
'always' becomes 'ever' (synonyms).
'cheerful' with its centre removed is 'cl'.
'cl'+'ever'='CLEVER'
(Other definitions for clever that I've seen before include "Smart, adroit" , "Deft, able, bright" , "brilliant" , "Quick at learning and understanding" , "Good or quick at learning" .)