The Latin word for friendship—amicitia—is derived from that for love—amor; and love is certainly the prime mover in contracting mutual affection.
 Marcus Tullius Cicero, On Friendship (44 BC). copy citation

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Author Marcus Tullius Cicero
Source On Friendship
Topic friendship love
Date 44 BC
Language English
Reference
Note Translated by E. S. Shuckburgh
Weblink http://www.gutenberg.org/files/2808/2808-h/2808-h.htm

Context

“Or is it not rather true that, although this is an advantage naturally belonging to friendship, yet its original cause is quite other, prior in time, more noble in character, and springing more directly from our nature itself? The Latin word for friendship—amicitia—is derived from that for love—amor; and love is certainly the prime mover in contracting mutual affection. For as to material advantages, it often happens that those are obtained even by men who are courted by a mere show of friendship and treated with respect from interested motives. But friendship by its nature admits of no feigning, no pretence: as far as it goes it is both genuine and spontaneous.” source