Keen to immerse husband in southern brook (6)
I believe the answer is:
shrill
'keen' is the definition.
(I've seen this before)
'husband in southern brook' is the wordplay.
'husband' becomes 'h'.
'in' means one lot of letters goes inside another.
'southern' becomes 's' (abbreviation).
'brook' becomes 'rill' (I've seen this before).
's'+'rill'='srill'
'h' inserted within 'srill' is 'SHRILL'.
'to immerse' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
(Other definitions for shrill that I've seen before include "Of voice, high-pitched and piercing" , "Of voice, highl-pitched and loud" , "High and piercing" , "Of sound, piercing and high-pitched" , "High-pitched and sharp" .)