Change three lenses, keeping very still (12)
I believe the answer is:
nevertheless
'still' is the definition.
(synonyms)
'change three lenses keeping very' is the wordplay.
'change' indicates an anagram.
'keeping' indicates putting letters inside.
'very' becomes 'v' (abbreviation).
'three'+'lenses'='threelenses'
'threelenses' is an anagram of 'neertheless'.
'neertheless' going around 'v' is 'NEVERTHELESS'.
(Other definitions for nevertheless that I've seen before include "In spite of everything" , "anyhow" , "at any rate" , "However" , "But always" .)