Akademik

на радости
НА РАДОСТЯХ (РАДОСТИ) coll
[PrepP; these forms only; adv]
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thanks to or because of one's elevated mood (on the occasion of a joyful event):
- in one's joy (rejoicing);
- from sheer joy;
- in celebration;
- to celebrate;
- elated (, one does sth.).
     ♦ Обыкновенно или чиновник умирал, или государь - и тогда наследник на радостях прощал долги (Герцен 2). Usually either the official died or the Tsar did, and then in his rejoicing the heir forgave the debts (2a)
     ♦ "Постой-ка, угощу тебя", - бессвязно бормотала она, доставая из сундука хранившуюся с давнишних пор бутылку самогона. Прохор присел, разгладил усы. "Ты-то выпьешь со мной на радостях?" - спросил он (Шолохов 5). "Just a minute, I've got something here for you..." she mumbled, rummaging in the chest for a bottle of home-brew that she had been keeping for many a long day. Prokhor sat down and stroked his moustache. "You'll have one with me to celebrate, won't you?" he asked (5a).

Большой русско-английский фразеологический словарь. — М.: ACT-ПРЕСС КНИГА. . 2004.