Office is out at sea catching cod, ultimately (6)
I believe the answer is:
studio
'office' is the definition.
(thesaurus)
'is out at sea catching cod ultimately' is the wordplay.
'at sea' indicates anagramming the letters.
'catching' means one lot of letters goes inside another.
'ultimately' suggests the final letters.
The last letter of 'cod' is 'd'.
'is'+'out'='isout'
'isout' with letters rearranged gives 'stuio'.
'stuio' placed around 'd' is 'STUDIO'.
(Other definitions for studio that I've seen before include "TV room?" , "Type of apartment without a separate bedroom" , "Apartment with one main room" , "Artist's work room" , "Film company - artist's atelier" .)