Single
It is used as a single word. Compound adjectives with the -ed form are always hyphenated or spelled as one word. (Absent-minded is occasionally found as a single word without a hyphen.)
Generosity - Liberality in giving or willingness to give spare forebear (verb only) spare and part with (but not a single word)
A single word that can be defined as (or otherwise signifies)'too important to be done without' is 'necessary.' When and where something is 'too important to be done without,' that same something is 'necessary.'
cleverness
My family has a interest in sports.
Perfunctory
Silent.
Aloof
atheist
holistic
Single
The verb, astonish, might do.
Sure! Run, jump, eat, sleep, read, write, and swim are examples of single-word verbs.
Not all bonds pay out interest through coupon payments.
We shall discuss changes in properties selected for their particular interest.
Volunteer.