Think about complete tan when swimming (11)
I believe the answer is:
contemplate
'think about' is the definition.
(to contemplate something is to think about it)
'complete tan when swimming' is the wordplay.
'when swimming' indicates an anagram.
'complete'+'tan'='completetan'
'completetan' anagrammed gives 'CONTEMPLATE'.
(Other definitions for contemplate that I've seen before include "Ponder" , "Intend" , "Think seriously" , "Look at thoughtfully" , "Consider" .)