Lewis Short
(adjective) : substillus, a, um, sub - stillo (ante- and post - class.)
* Slightly dropping, dribbling.
* Adj.: lotium,i. e. strangury,Cato, R. R. 156, 6.
* Subst.: substil-lum, i, n., a slight dropping, a sprinkling: substillum tempus ante pluviam jam paene uvidum et post pluviam non persiccum, quod jam stillaret, aut nondum desisset, Fest. pp. 306 and 307 Müll.: dehinc substillum et denuo sudum,Tert. Pall. 2.
Charlton T. Lewis, Charles Short, A Latin Dictionary