regrettable

As an adverb regretable

is an alternative spelling of regrettable.

As an adjective regrettable is

of an event, action, or state, allowing or deserving regret.

As a noun taxonomy

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

As an adjective regrettable is

of an event, action, or state, allowing or deserving regret.

As adjectives the difference between lamentable and regrettable

is that lamentable is causing sorrow, distress or regret; deplorable, pitiful or distressing while regrettable is of an event, action, or state, allowing or deserving regret.

As adjectives the difference between deplorable and regrettable

is that deplorable is deserving strong condemnation; shockingly bad while regrettable is of an event, action, or state, allowing or deserving regret.