Alternative words you could use instead of the word…

Plain

As an adjective

Specifically meaning clear, straight to the point.

Aboveboard

Abrupt

Artless

Bluff

Blunt

Brusk

Brusque

Candid

Curt

Direct

Ernest

Forthright

Foursquare

Frank

Freespoken

Gruff

Honest

Impolite

Inconsiderate

Open

Openhearted

Outspoken

Plainspoken

Pointblank

Rude

Sharp

Sincere

Straight

Straightforward

Tactless

True

Truthful

Undiplomatic

Guarded

Uninhibited

Unreserved

Unrestrained

Veracious