Work out velocity, initially, alone outside? (5)
I believe the answer is:
solve
'work out' is the definition.
(thesaurus)
'velocity initially alone outside?' is the wordplay.
'initially' indicates taking the first letters.
'alone' becomes 'sole' ('sole' can be a synonym of 'alone').
'outside?' indicates putting letters inside.
The initial letter of 'velocity' is 'v'.
'v' inserted inside 'sole' is 'SOLVE'.
(Other definitions for solve that I've seen before include "Loves (anag) - to find an answer" , "Find the answer to a puzzle" , "Find the 3dn to a mystery" , "Find the answer to this clue, for instance" , "Crack clues" .)