To inform on someone to the authorities, teachers, or a boss (его заложил собственный сообщник — “he was ratted out by his own accomplice”).
Зато готова была заложить боевого товарища, все таки взгляд на жизнь у наших ребят и у нее совершенно разный.
However, she was ready to betray a comrade-in-arms, as her outlook on life is completely different from that of our guys.
(rusalochhka @ 1tv.ru, 11/2011)
