Willing female volunteers in experiment, one run by hosts (9)
I believe the answer is:
testatrix
'willing female' is the definition.
The definition and answer can be both people as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'volunteers in experiment one run by hosts' is the wordplay.
'volunteers' becomes 'TA' (abbreviation for Territorial Army).
'in' indicates putting letters inside.
'experiment' becomes 'test' (test is a kind of experiment).
'one run' becomes 'r' (cricket abbreviation).
'by hosts' becomes 'ix' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ta' inserted within 'test' is 'testat'.
'testat'+'r'+'ix'='TESTATRIX'
Can you help me to learn more?
(Other definitions for testatrix that I've seen before include "A woman who has made a will" , "Woman willing" .)