Moored and set about task (8)
I believe the answer is:
anchored
'moored' is the definition.
(thesaurus)
'and set about task' is the wordplay.
'set about' indicates putting letters inside.
'task' becomes 'chore' (synonyms).
'and' going around 'chore' is 'ANCHORED'.
(Other definitions for anchored that I've seen before include "firmly secured in position" , "Made fast, secured" , "Ron ached (anag.)" , "secure so?" , "In immovable position" .)