Group without Lemmy's lead is dull (5)
I believe the answer is:
bland
'dull' is the definition.
(similar in meaning)
'group without lemmy's lead' is the wordplay.
'group' becomes 'band' (band can mean a group of people).
'without' indicates putting letters inside ('without' can be similar in meaning to 'outside').
'lead' says to take the initial letters.
The first letter of 'lemmy' is 'l'.
'band' placed around 'l' is 'BLAND'.
'is' is the link.
(Other definitions for bland that I've seen before include "Insipid, vapid" , "Boring" , "Mild; dull" , "Lacking taste, flavour" , "Insipid, banal" .)