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adj. Not disposed to expressions of feeling; reserved.

adj. not given to showing emotion or feelings; reserved or distant

Not demonstrative or given to excited or strong expression of feeling; reserved, from modesty, diffidence, or policy: as, an undemonstrative person; undemonstrative manners.

adj. not given to open expression of emotion

"Even when it is a practical, living thing that can be felt and built on, it is often almost cold-bloodedly inarticulate and undemonstrative, which is the only kind of sympathy acceptable to a man in trouble, especially a man of Druro's type, who did not want to discuss the thing at all, but just to take what was coming to him with a stiff lip."

reticent    unemotional    restrained   

impassive   

scatter-brained    overmodest    reticent    unpretentious    simple-mannered