As adjectives the difference between grassiest and gassiest
is that grassiest is (grassy) while gassiest is (gassy).
grassiest
English
Adjective
(head)
(grassy)
grassy
English
Adjective
(er)
Covered with grass.
Resembling grass.
gassiest
English
Adjective
(head)
(gassy)
gassy
English
Adjective
(er)
Of a beverage, containing dissolved gas (usually carbon dioxide).
Flatulent.
Synonyms
* (of a beverage, containing gas ): fizzy