Adolescence /ˌæd

It seemed pointless to continue.
informal It 's pointless argu ing with him.
pristine /ˈprɪs.tiːn/ /prɪˈstiːn/ adjective formal approving
new or almost new, and in very good condition
pristine new offices
Washing machine for sale - only 2 months old and in pristine condition .
questionable /ˈkwes.tʃə.nə.bl ̩/ adjective [ + question word ]
not certain, or wrong in some way
It is questionable wh ether this goal can be achieved.
Much of late-night television is of questionable value/taste .
recyclable /ˌriːˈsaɪ.klə.bl ̩/ adjective
able to be recycled
recycled /ˌriːˈsaɪ.kl ̩d/ adjective
having been used before and then processed so that it can form a new product
This newspaper is made of recycled paper .
sustainable /səˈsteɪ.nə.bl ̩/ adjective
1. able to continue over a period of time
That sort of extreme diet is not sustainable over a long period.
2. causing little or no damage to the environment and therefore able to continue for a long time
A large international meeting was held with the aim of promoting sustainable development in all countries.
taxing /ˈtæk.sɪŋ/ adjective
difficult or needing a lot of thought or effort
I like a bit of light reading when I'm on holiday - nothing too taxing.
unattainable /ˌʌn.əˈteɪ.nə.bl ̩/ adjective
not able to be achieved
an unattainable ideal
Some economists think that full employment in Europe is an unattainable goal .
unlikely /ʌnˈlaɪ.kli/ adjective
not likely
[ + ( that ) ] It 's pretty unlikely (that) they'll turn up now - it's nearly ten o'clock.
He seems an unlikely-looking policeman (= He is not what I expect a policeman to look like) .
unprecedented /ʌnˈpres.ɪ.den.tɪd/ /-t ̬ɪd/ adjective
never having happened or existed in the past
This century has witnessed environmental destruction on an unprecedented scale .
useless /ˈjuː.sləs/ adjective
of no use; not working or not achieving what is needed
Without fuel, the vehicles will become useless for moving supplies.
[ + to infinitive ] It's useless to speculate without more information.
She's very good at methodical work, but useless when there's a lot of pressure.
informal You're absolutely useless (= not able to act effectively) - can't you even go to the shops without getting lost!
viable /ˈvaɪ.ə.bl ̩/ adjective
1. able to work as intended or able to succeed
In order to make the company viable, it will unfortunately be necessary to reduce staffing levels.
I am afraid your plan is not commercially/economically/financially/politically viable.
2. specialized able to continue to exist as or develop into a living being
There is a continuing debate about the age at which a human fetus can be considered viable.