1 call upon to appear, esp. as a defendant or witness in a lawcourt.
2 (usu. foll. by to + infin.) call upon (summoned her to assist).
3 call together for a meeting or some other purpose (summoned the members to attend).
Phrases and idioms:
summon up (often foll. by to, for) gather (courage, spirits, resources, etc.) (summoned up her strength for the task).
Derivatives:
summonable adj. summoner n.
Etymology: ME f. OF somondre f. L summonere (as SUB-, monere warn)
Useful english dictionary. 2012.