Being big is wonderful (5)
I believe the answer is:
great
I believe this is a double definition.
'being big' is the first definition.
(similar in meaning)
'wonderful' is the second definition.
(I've seen this before)
'is' is the link.
(Other definitions for great that I've seen before include "1963 Buckinghamshire mail van raid" , "Storage container" , "Considerably above average" , "Mum's dad's mum, for example" , "and 12 Down: Powerful dog" .)