... As moving cranes pick one (7)
I believe the answer is:
arsenic
'as' is the definition.
(As is the chemical symbol for arsenic)
'moving cranes pick one' is the wordplay.
I cannot really see how this works, but
'one' could be 'i' (roman numeral) and 'i' is found in the answer.
an anagram of 'cranes' is 'arsenc' which is present in the remaining letters.
No letters remain.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for arsenic that I've seen before include "Toxic metallic element used as rat poison" , "As briefly identified" , "-- and Old Lace (play)" , "Powerful poison" , "Toxic metalloid element" .)