Pay due regard to board (4)
I believe the answer is:
keep
I believe this is a double definition.
'pay due regard to' is the first definition.
(as in keeping a promise)
'board' is the second definition.
(both can mean payment for lodgings)
(Other definitions for keep that I've seen before include "honour" , "Main tower within the walls of a castle" , "Retain or care for" , "Eg, beef" , "Remain" .)