Dictionary Definition :
Definition[1]
:
Now a 眞言 Shingon term; the 四教 are the Tiantai four schools of 顯 open or exoteric teaching; the 三密 are the Shingon esoteric teaching in which the three 身口意 body, mouth, and mind have special functions.
Source
:
A Dictionary of Chinese Buddhist Terms, William Edward Soothill and Lewis Hodous
Definition[2]
:
四教三密===(術語)身口意之三業也。是真言密教之教之妙行。故四教三密,為顯(天台)密(真言)二教之兼稱。
Source
:
丁福保《佛學大辭典》