Silent, uncommunicative, taciturn, reticent, reserved, secretive, close, close-lipped, closemouthed, tight-lipped are comparable when they mean showing restraint in speaking to or with others.
Silent and uncommunicative often imply a tendency to say no more than is absolutely necessary as a matter of habit or an abstinence from speech on some particular occasion typically because of caution or the stress of emotion.
Taciturn implies a temperamental disinclination to speech; it usually also connotes unsociableness or the nature of one who grudgingly converses when necessary.
Reticent implies the disposition to keep one’s own counsel or the habit or fact of withholding much that might be said, especially under particular circumstances; the term does not usually connote silence but, rather, sparing speech or an indisposition to discuss one’s private affairs.
Reserved implies reticence but it also suggests formality, standoffishness, or a temperamental indisposition to the give and take of friendly conversation or familiar intercourse.
Secretive also implies reticence, but it adds an implication of disparagement that reticent usually lacks, for it suggests an opposition to frank or open and often connotes an attempt to hide or conceal something that might properly be told.
Close (see also CLOSE 1 & CLOSE 2 ) comes near to reticent and secretive in its meaning but it usually denotes a disposition rather than an attitude or manner and, therefore, often suggests taciturnity.
Close-lipped and closemouthed are often used in place of close not only as more picturesque terms but also as more clearly implying a determined refusal to disclose something that another desires to know.
Tight-lipped carries a stronger implication of resolute but not necessarily temperamental reticence.