A-E-I-O-U

Nice straightforward one - all the answers contain all the vowels, but no vowel is used more than once. Simples...

As ever, I'm all heart and have given you the word length and the first letter

-1. Group of people acting on the behalf of others (10, D)
-2. Clear, without exceptions (11, U)
-3. Percussion instrument (10, T)
-4. Coniferous tree (7, S)
-5. Extreme weariness (10, E)
-6. Unnecessarily wary (12, O)
-7. Dubious (12, Q)
-8. Fame, notoriety (10,R)
-9. Timid, unassertive person (11, M)
-10. Concurrent (12, S)

10 - simultaneous

3. tambourine

Hi Rog.

A great family start!

1. deputation

You got it, michele!

2. unequivocal

Yes, Joan!

8. reputation

5. exhaustion

4. sequoia

7. questionable

Great selection, everybody!

I was getting ready to answer #7 earlier today and then I did not post it, because I realized that "questionable" has two of the letter E in it. I thought there was only supposed to be one vowel each?

Anyway, how about:

9. milquetoast

I did the same thing Marian. I posted it and then I took it off and I edited several times until I realized that there are some other answers that also use the same vowel twice so I reposted my answer.

Good to know, oldbroad.

6. overcautious

Ah. Methinks I smell tar being heated up and hear the sound of chickens being plucked

No excuses other than fullblown incompetence. I shall go away and give myself a thorough chastisement with Pandora's wet noodles. Praise to all those who mangaed correct answers despite the confusion

No worries, Rog!

No harm done!