A month at work on the sea bed (7)
I believe the answer is:
octopus
'the sea bed' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'a month at work' is the wordplay.
'a month' becomes 'oct' (Oct is an example).
'at' says to put letters next to each other.
'work' becomes 'opus' (I've seen this before).
'oct'+'opus'='OCTOPUS'
'on' is the link.
Can you help me to learn more?
(Other definitions for octopus that I've seen before include "Marine cephalopod" , "Tentacled cephalopod" , "pernicious organisation" , "Creature with eight tentacles" , "Creature with eight limbs" .)