Beneath sea one finds tarry anchor (8)
I believe the answer is:
mainstay
'anchor' is the definition.
(I know that anchor can be written as mainstay)
'beneath sea one finds tarry' is the wordplay.
'beneath sea' becomes 'main' (synonyms. I am not sure about the 'beneath' bit.).
'one finds' means one lot of letters go next to another.
'tarry' becomes 'stay' (I've seen this in another clue).
'main'+'stay'='MAINSTAY'
Can you help me to learn more?
(Other definitions for mainstay that I've seen before include "Strong cable that secures a mast, chief support generally" , "Bulwark" , "Pillar of strength" , "Strongest support" , "Chief source of support" .)