restrained

Synonyms: bottled up calm and collected chilled conservative controlled cool corked up discreet in charge in check inobtrusive laid-back mild moderate muted on a leash plain reasonable reticent retiring self-controlled shrinking soft steady subdued tasteful temperate unaffable undemonstrative under control under wraps unexcessive unexpansive unextreme unobtrusive uptight withdrawn

Antonyms: assured bold confident extroverted outgoing