Dull time aboard to do with nerves (7)
I believe the answer is:
neutral
'dull' is the definition.
(thesaurus)
'time aboard to do with nerves' is the wordplay.
'time' becomes 't'.
'aboard' means one lot of letters goes inside another.
'to do with nerves' becomes 'neural' (I've seen this before).
't' put into 'neural' is 'NEUTRAL'.
(Other definitions for neutral that I've seen before include "A runlet? (anag)" , "Impartial r" , "Impartial; beige" , "trying to keep out of the war" , "On the fence" .)