Left in sea — could become this? (6)
I believe the answer is:
saline
'this?' is the definition.
The definition suggests a singular noun which matches the answer.
'left in sea could become' is the wordplay.
'left' becomes 'l' (common abbreviation).
'could become' indicates anagramming the letters.
'l'+'in'+'sea'='linsea'
'linsea' is an anagram of 'SALINE'.
Can you help me to learn more?
(Other definitions for saline that I've seen before include "solution" , "Containing salt for aliens" , "Salty like sea water" , "Salty to aliens" , "Containing salt or salts" .)