### Clue: In 1999 I will move tree a short distance (10)
### Answer: MILLIMETRE 
 ### Explanation: Definition: a short distance
An envelope ('in') of I'LL ('I will') in MIM (as a subject that has been touched on before in these hallowed halls, this is not a canonical formation, so let us call it a Romanesque numeral, '1999') plus ETRE, an anagram ('move') of 'tree'.