At first, the co-workers are intimidating (3)
I believe the answer is:
cow
'are intimidating' is the definition.
I can't tell whether this defines the answer.
'at first the co-workers' is the wordplay.
'at first' means one lot of letters go next to another.
'workers' becomes 'w' (this might be a standard abbreviation I've not previously seen).
'co'+'w' is 'COW'.
Can you help me to learn more?
(Other definitions for cow that I've seen before include "Browbeat" , "female whose homecoming is indefinitely delayed" , "Subdue with threats or force" , "Source of milk" , "frighten as with threats" .)