unconcern

As an adjective complacent

is uncritically satisfied with oneself or one's achievements; smug.

As a noun unconcern is

(nonstandard|obsolete) indifference or lack of concern.

As a noun unconcern

is (nonstandard|obsolete) indifference or lack of concern.

As an adjective undefined is

lacking a definition or value.

Unfeelingness is a related term of unconcern.

As nouns the difference between unfeelingness and unconcern

is that unfeelingness is the state or condition of being unfeeling while unconcern is (nonstandard|obsolete) indifference or lack of concern.

Unconcern is a related term of sluggishness.

As nouns the difference between unconcern and sluggishness

is that unconcern is (nonstandard|obsolete) indifference or lack of concern while sluggishness is the property of being sluggish, unable or unwilling to act quickly.

As nouns the difference between disinterest and unconcern

is that disinterest is (obsolete) what is contrary to interest or advantage; disadvantage while unconcern is (nonstandard|obsolete) indifference or lack of concern.

As a verb disinterest

is to render disinterested.

As an adjective disinterest

is (obsolete) disinterested.

As a noun unconcern

is (nonstandard|obsolete) indifference or lack of concern.

As an adjective apathetic is

void of feeling; not susceptible of deep emotion; passionless; indifferent.

As an adjective insensible

is unable to be perceived by the senses.

As a noun unconcern is

(nonstandard|obsolete) indifference or lack of concern.

Unconcern is a related term of insensibility.

As nouns the difference between unconcern and insensibility

is that unconcern is (nonstandard|obsolete) indifference or lack of concern while insensibility is the property of being insensible.

As an adjective uncurious

is incurious.

As a noun unconcern is

(nonstandard|obsolete) indifference or lack of concern.