regretful

As a noun taxonomy

is the science or the technique used to make a classification.

As an adjective regretful is

full of feelings of regret, indulging in regrets.

Pityful is likely misspelled.

Pityful has no English definition.

As an adjective regretful is

full of feelings of regret, indulging in regrets.

Regrettabe is often a misspelling of regretful.

Regrettabe has no English definition.

As an adjective regretful is

full of feelings of regret, indulging in regrets.

As adjectives the difference between regretful and repentant

is that regretful is full of feelings of regret, indulging in regrets while repentant is feeling or showing sorrow for wrongdoing.

As a noun repentant is

one who repents; a penitent.

As adjectives the difference between regretful and pitiful

is that regretful is full of feelings of regret, indulging in regrets while pitiful is feeling pity; merciful.