considerable, deep, grave, great, major, serious | growing, mounting | common, widespread | national, public
public concern about increased taxes

feel
He felt some concern for her safety.

express, show, voice | cause
The lack of firefighting equipment has caused concern.

in sb''s ~
She forgot her own worries in her concern for him.

out of ~ | ~ about/over
She expressed her deep concern about conditions at the factory.

~ for
Out of concern for her health, we suggested she take a week off work.

be of (no) concern to sb
Increased use of drugs is of great concern to parents.

(a) cause for concern
The president''s health is giving serious cause for concern.

a lack of concern
I was surprised by her lack of concern.

a matter of concern
Stress at work is a matter of concern to staff and management.

chief, main, major, overriding, paramount, primary
What are your main concerns as a writer?

common
a common concern for new parents

be none of sb''s concern
How much we paid is none of your concern.

directly

in
Everyone who was directly concerned in (= had some responsibility for) the incident has now resigned.

a lot, really
It really concerns me that he doesn''t eat properly.

slightly