"Alliteration" is a twelve letter word.
That adjective may be classic.
A 5 letter word that starts with an L is Lipid
The word you are looking for is DISCOUNT.(which as an adjective discount or discountedmeans less than full price)
A six letter word that starts with U is upward.
unknowingly unassuming unconscious unaccessible
pessimistic
scholastic
A canal is aquatic. The adjective begins with the letter a.
diurnal, daily
ceelecsstrail
It must be a word (adjective) that starts with a letter in responsibility and describes responsibility.
chauvinisticcatastrophic
Snowflakes can be described as lightweight. The adjective begins with the letter l.
Native as an adjective is one
The smell from a gas leak reeks. The adjective begins with the letter r.
Earthquakes