Go off at a tangent about son in lodgings (7)
I believe the answer is:
digress
'go off at a tangent' is the definition.
(I've seen this before)
'about son in lodgings' is the wordplay.
'about' becomes 're' (regarding**).
'son' becomes 's'.
'in' indicates putting letters inside.
'lodgings' becomes 'digs' ('digs' can be a synonym of 'lodgings').
're'+'s'='res'
'res' placed within 'digs' is 'DIGRESS'.
(Other definitions for digress that I've seen before include "Ramble" , "Go off the main subject" , "Turn aside (from the main subject?)" , "Depart from the main subject" , "Leave the main subject" .)