Thought of liner, etc, at sea (10)
I believe the answer is:
reflection
'thought' is the definition.
(reflection is a kind of thought)
'of liner etc at sea' is the wordplay.
'at sea' is an anagram indicator.
'of'+'liner'+'etc'='oflineretc'
'oflineretc' anagrammed gives 'REFLECTION'.
(Other definitions for reflection that I've seen before include "Effect of not absorbing light" , "Mirror image" , "serious thought?" , "mental study's required" .)