Called head of year lanky (5)
I believe the answer is:
rangy
'lanky' is the definition.
(I know that lanky can be written as rangy)
'called head of year' is the wordplay.
'called' becomes 'rang' (called on the phone).
'head of' indicates taking the first letters.
The first letter of 'year' is 'y'.
'rang'+'y'='RANGY'
(Other definitions for rangy that I've seen before include "Tall, slim, long-limbed" , "Having long, slender limbs" , "Gangling" , "Antipodean mountain" , "with long legs" .)