Submarine inside founders easily (8)
I believe the answer is:
undersea
'submarine' is the definition.
(synonyms)
'inside founders easily' is the wordplay.
'inside' indicates the answer is hidden within the clue.
'UNDERSEA' is hidden within 'founders easily'.
(Other definitions for undersea that I've seen before include "Below marine surface" , "in salt water" , "Submarine" , "Beneath the surface of the ocean" , "Beneath the oceans" .)