verb/mu.ja.se/
to rain on and off, to drizzle, to sprinkle
“On espérait une grosse pluie, mais ç’a juste mouillassé un petit brin.” — We were hoping for a big rain, but it just drizzled a little bit.
Related: mouillassant, mouillasse, mouillasserie, mouillasseux
mouille(r) (“to rain”) + -asser (frequentative suffix)