taciturn
unassertive
undemonstrative
Olympian
aloof
backward
bashful
blank
chilled
chilly
close
close-lipped
close-tongued
closed
closemouthed
cold
constrained
cool
dark
detached
discreet
distant
dumb
expressionless
forbidding
frigid
frosty
guarded
icy
impassive
impersonal
inaccessible
introverted
modest
mum
offish
private
quiet
remote
removed
repressed
reserved
restrained
retiring
secret
secretive
shrinking
shy
silent
standoff
apprehensive
averse
cautious
circumspect
docile
downcast
hesitant
morose
observant
respectful
sedate
self-possessed
timorous
uncommunicative
unsure
wary
watchful
communicative
talkative