Tendency of doctor to go on one foot (5)
I believe the answer is:
drift
'tendency' is the definition.
(I know that drift is a type of tendency)
'doctor to go on one foot' is the wordplay.
'doctor' becomes 'Dr' (abbreviation).
'to go on' says to put letters next to each other (in a down clue, some letters go on top of others).
'one' becomes 'i' (Roman numeral).
'foot' becomes 'ft' (abbreviation).
'dr'+'i'+'ft'='DRIFT'
'of' is the link.
(Other definitions for drift that I've seen before include "Import" , "Trend; meaning" , "go with the tide" , "General trend - current travel" , "Travel without purpose" .)