Wiktionary
prep. (context UK English) for; for the sake of - usually placed at the end of a question when quizzing a person about why they have done something.
Usage examples of "in aid of".
It contained particulars of his interviews with several other nobles, with details as to the number of men they could put in the field, and the funds they could dispose of in aid of the rising.
While the war was carried on between Louis and Charles in Puglia, new forces were sent from France in aid of Louis, and on arriving in Tuscany, were by the emigrants of Arezzo conducted to that city, and took it from those who held possession for Charles.
Nor would he, when they met him at his own house, or that of Phillips, as they several times did, that winter, to compare the discoveries and observations they had made, and discuss the subject, any longer maintain the position he at first so boldly took, respecting Gaut's guilt, or say any thing in aid of their deliberations.
With Preia Starle, they talked of what Tay had hoped to accomplish and how they must see that his goals were realized-to see that the Black Elfstone reached Bremen and that the Elven army was dispatched in aid of the Dwarves.