Point of no return for one held by Polish prisoner? (7)
I believe the answer is:
rubicon
'point of no return' is the definition.
('Rubicon' can be a synonym of 'point of no return')
'one held by polish prisoner?' is the wordplay.
'one' becomes 'i' (Roman numeral).
'held by' indicates putting letters inside.
'polish' becomes 'rub' (polish meaning rub to make shiny).
'prisoner?' becomes 'con' (abbreviation for 'convict').
'rub'+'con'='rubcon'
'i' put inside 'rubcon' is 'RUBICON'.
'for' is the link.
(Other definitions for rubicon that I've seen before include "Caesar's fateful river" , "River, its crossing decisive" , "ancient border" , "River crossed by Caesar - no turning back" , "No, I curb the fateful river" .)