As nouns the difference between jemmy and jelly
is that
jemmy is (archaic|british|slang) a baked sheep's head while
jelly is (new zealand|australia|british) a dessert made by boiling gelatine, sugar and some flavouring (often derived from fruit) and allowing it to set.
As verbs the difference between jemmy and jelly
is that
jemmy is to shoehorn, to cram while
jelly is to wiggle like jelly.
As adjectives the difference between jemmy and jelly
is that
jemmy is (archaic) of spruce while
jelly is (slang) jealous.