WordNet sense 1 (marked by avoidance of extravagance or extremes):

moderate, moderate

WordNet sense 2 (not extreme in behavior):

temperate

WordNet sense 3 (restrained in style or quality):

subdued

WordNet sense 4 (not showy or obtrusive):

quiet

WordNet sense 5 (not ostentatious):

unpretentious, unostentatious, unpretending

WordNet sense 6 (free from ostentation or pretension):

modest

WordNet sense 7 (marked by prudence or modesty and wise self-restraint):

discreet

WordNet sense 8 (cool and formal in manner):

reserved, reticent, unemotional

WordNet sense 9 (not given to open expression of emotion):

undemonstrative

WordNet sense 10 (showing careful forethought):

cautious

WordNet sense 11 (prudent):

guarded