_amicitiam cum aliquo jungere, facere, inire, contrahere_—to form a
friendship with any one.
_amicitiam colere_—to keep up, foster a connection.
_uti aliquo amico_—to be friendly with any one.
_est_ or _intercedit mihi cum aliquo amicitia_—I am on good terms with
a person.
_sunt_ or _intercedunt mihi cum aliquo inimicitiae_[1]—I am on bad
terms with a person.
_uti aliquo familiariter_—to be on very intimate terms with...
_artissimo amicitiae vinculo_ or _summa familiaritate cum aliquo
coniunctum esse_—to be bound by the closest ties of friendship.
_vetustate amicitiae coniunctum esse_—to be very old friends.
_amicitiam alicuius appetere_—to court a person's friendship.
_in amicitiam alicuius recipi_—to gain some one's friendship; to
become intimate with.
_ad alicuius amicitiam se conferre, se applicare_—to gain some one's
friendship; to become intimate with.
_aliquem (tertium) ad (in) amicitiam ascribere_—to admit another into
the circle of one's intimates.
_amicitiam renuntiare_—to renounce, give up a friendship.
_amicitiam dissuere, dissolvere, praecīdere_—to renounce, give up a
friendship.
_amicissimus meus_ or _mihi_—my best friend.
_homo intimus, familiarissimus mihi_—my most intimate acquaintance.
_inimicitias gerere, habere, exercere cum aliquo_—to be at enmity with
a man.
_inimicitias cum aliquo suscipere_—to make a person one's enemy.
_inimicitias deponere_—to lay aside one's differences.
_aequi iniqui_—friend and foe.
_placare aliquem alicui_ or _in aliquem_—to reconcile two people; to
be a mediator.
_reconciliare alicuius animum_ or simply _aliquem alicui_—to reconcile
two people; to be a mediator.
_in gratiam aliquem cum aliquo reducere_—to reconcile two people; to
be a mediator.
_in gratiam cum aliquo redire_—to be reconciled; to make up a quarrel.
_sibi aliquem, alicuius animum reconciliare_ or _reconciliari
alicui_—to be reconciled; to make up a quarrel.
[1] The singular _inimicitia_ is only used to express the abstract
idea "enmity".