As a noun headmaster
is (chiefly|uk) a male school principal.
As an adjective headmasterly is
in a manner befitting a headmaster.
Other Comparisons: What's the difference?
(chiefly, UK) A male school principal.
The term is gender-specific, and refers to a male in the position. A female in the same role would be called a headmistress .
In a manner befitting a headmaster.
* 2008 , Robin Darwall-Smith, A History of University College, Oxford
- Bradley had to learn that headmasterly wrath did not work on undergraduates like Charles Cree.