Pole beginning to toast cockney's well-being in secrecy (7)
I believe the answer is:
stealth
'being in secrecy' is the definition.
(I've seen this before)
'pole beginning to toast cockney's well' is the wordplay.
'pole' becomes 's' (abbreviation for South, as in South Pole).
'beginning to' suggests taking the first letters.
'cockney's well' becomes ''ealth' ('health' - I've seen this before - said with a cockney accent, dropping the 'H').
The first letter of 'toast' is 't'.
's'+'t'+'ealth'='STEALTH'
(Other definitions for stealth that I've seen before include "word to define secrecy" , "Low-visibility military technology" , "Unseen machination" , "The last (anag.)" , "Avoidance of detection by moving carefully" .)