One fluid in another, it seems to me (8)
I believe the answer is:
methinks
'one fluid in another it' is the definition.
I can't judge whether this defines the answer.
'seems to me' is the wordplay.
'seems' becomes 'thinks' (I can't justify this - if you can you should believe this answer much more).
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'thinks' after 'me' is 'METHINKS'.
(Other definitions for methinks that I've seen before include "I believe" , "I gather" , "I reckon" , "In my view - knit hems (anag)" , "I feel ..." .)