1 n. — Education
a graduation ceremony, usually for universities.
Type: 3. Semantic Change — This meaning of convocation evolved from the general meaning of 'the state of being called together' (see OED-3, s.v. "convocation" (1)) and 'an assembly of the University' (see OED-3, s.v "convocation" (4a)). It is likely a semantic development from the term used for the legislative assemblies of the English universities, which adopted the meaning from ecclesiastical meetings. It was also used in Canada for what are now called high school graduation ceremonies (see the 1900 quotation).
In the British university system, these ceremonies are called degree or graduation ceremonies, while at American universities, the event is usually called a commencement. Some US universities have both ceremonies, where the commencement is a university-wide event and the convocation is for individual colleges presenting degrees to graduate-level individuals (see also University of Oklahoma reference).
See also COD-2, s.v. "convocation" (1), which is marked " N. Amer", OED-3, s.v. "convocation" (4a), which is marked "In the English Universities", W-3, s.v. "convocation" (d(2)), which is marked "at some Canadian universities".
2 n. — Administration
a provincial law society's governing council.
Type: 3. Semantic Change — This meaning of convocation is marked as Canadian in the COD-2, and it is very similar to the general definition of 'an assembly of people called together' (see OED-3, s.v. "convocation" (2)). This meaning has specialized to refer to a meeting of governing officials of law societies in Canada, who are also known as benchers (see entry).
See also COD-2, s.v. "convocation" (3), which is marked "Cdn Law".