Dictionary Definition :
Definition[1]
:
The four large circles in each of which the thirty-seven are represented, in one all hold the diamond-realm symbol, the vajra; in another, the symbol relating to the triple realm of time, past, present, future; in another, the Guanyin symbol; and in another, the symbol of infinite space.
Source
:
A Dictionary of Chinese Buddhist Terms, William Edward Soothill and Lewis Hodous
Definition[2]
:
(名數)金剛頂十八會之第一教王會有四大輪:一、金剛界輪,三十七尊皆持金剛之印。二、降三世教令輪,三十七尊皆持降三世之印。三、遍調伏法輪,三十七尊皆持觀世音之印。四、一切義成就輪,三十七尊皆持虛空藏之印。見瑜祇經疏二。
Source
:
丁福保《佛學大辭典》