【Familiar】 ,  【intimate】 ,  【close】 ,  【confidential】 ,  【chummy】 ,  【thick】  are comparable when meaning near to one another because of constant or frequent association, shared interests and activities, or common sympathies, or, when applied to words or acts, indicative of such nearness.

【Familiar】  suggests relations or manifestations characteristic of or similar to those of a family, where long-continued intercourse makes for freedom, informality, ease of address, and the taking of liberties; consequently  【familiar】 may apply to the relations, words, and acts of persons actually in such a situation and to the attitude or the style of speaking or writing of persons who assume the freedom and ease of address of those who are.

【Intimate】 suggests relations characteristic of those who are in 【close】 contact with one another (as through ties of blood, of friendship, or of common interests or aspirations) and who have opened their hearts or their minds to such a degree that they deeply know and understand one another.

【Intimate】 may also apply to a connection between a person and a thing, especially something he says, does, wears, or uses; it then implies a very 【close】 relation between that thing and his inmost thoughts or feelings or his life in the privacy of his home.

As applied directly or indirectly to knowledge, 【intimate】  differs from  【familiar】 not only in idiom but also in implying not merely acquaintance but 【close】 or deep study.

【Close】  is often used in place of  【intimate】 when one wishes to imply an attachment drawing persons together in such a way as to suggest the exclusion of others or a very strong bond of affection between them.

【Confidential】 implies a relationship based upon mutual trust or confidence or upon a willingness to confide 【intimate】 matters (as one’s hopes, thoughts, or feelings).

【Chummy】  and  【thick】  are less formal terms and usually convey some degree of contempt, derision, or envy of a 【close】 association.

【Chummy】 suggests an easy informal intimacy.

【Thick】 stresses constant association more than the strength of the attachment, but often it carries a sinister suggestion.