Trust European leaving part of swimming pool? (6)
I believe the answer is:
depend
'trust' is the definition.
(I know that depend is a more specific form of the action the trust)
'european leaving part of swimming pool?' is the wordplay.
'european' becomes 'E' (abbreviation e.g. EU).
'leaving' suggests deleting specific letters.
'part of swimming pool?' becomes 'deepend' (I've seen this before).
'deepend' with 'e' taken out is 'DEPEND'.
(Other definitions for depend that I've seen before include "Bank" , "Rely or hang on" , "Hang down or be connected to something" , "Be unable to do without, rely" , "Put trust (in)" .)