To plan together; to settle or adjust by conference, agreement, or consultation. / To plan; to devise; to arrange. / To act in harmony or conjunction; to form combined plans.

(uncountable) Agreement in a design or plan; union formed by mutual communication of opinions and views; accordance in a scheme; harmony; simultaneous action.

Used as a formal salutation in a letter when the writer does not know who will read the letter.

Causing concern; worrying. / (obsolete) Important.

Regarding, respecting.

present participle of concern

That which one is concerned in; one's business.

(transitive) To develop an idea; to form in the mind; to plan; to devise; to originate. / (transitive) To understand (someone). / (intransitive or transitive) To become pregnant (with).

(geometry) Having a common center.

curved like the inner surface of a sphere or bowl / (geometry, not comparable, of a polygon) not convex; having at least one internal angle greater than 180 degrees.