re- (expressing intensive force) + tacere ‘be silent’

SILENT, TACITURN, RETICENT, RESERVED, SECRETIVE mean showing restraint in speaking.

SILENT implies a habit of saying no more than is needed.

e.g. the strong, silent type

TACITURN implies a temperamental disinclination to speech and usually connotes unsociability.

e.g. taciturn villagers

RETICENT implies a reluctance to speak out or at length, especially about one's own affairs.

e.g. was reticent about his plans

RESERVED implies reticence and suggests the restraining influence of caution or formality in checking easy informal conversational exchange.

e.g. greetings were brief, formal, and reserved

SECRETIVE, too, implies reticence but usually carries a suggestion of deviousness and lack of frankness or of an often ostentatious will to conceal.

e.g. the secretive research and development division

source: [沈黙｜無料GIF画像検索 GIFMAGAZINE 3290320]

not revealing one's thoughts or feelings readily:

｟かたく｠ «…について» 寡黙な, 口の重い(silent) «about» ; 〈表現が〉控えめな

e.g. she was extremely reticent about her personal affairs.

reticently | ˈredəs(ə)ntlē | adverb

mid 19th century: from Latin reticent- ‘remaining silent’, from the verb reticere, from re- (expressing intensive force) + tacere ‘be silent’.