Other forms: summoned, summons, summoning
To summon someone is to order them to come, with authority behind the order. A court summons a witness, a headteacher summons a pupil, a king summons his generals. Nobody who has been summoned is free to say no.
It also means calling something up out of yourself: summon the courage, summon the energy, summon a smile for the camera. With 'up' it works on memories, as when a smell summons up a whole childhood. In stories you summon spirits and demons, which is where many learners meet the word first. Watch the noun, because it is a summons, with the s, and its plural is summonses; 'a summon' does not exist. The register is formal, so for ordinary asking use call or ask someone to come.
1verbsummonTo order someone to come, especially by official authority.
“She was summoned to the manager's office before lunch.”
formal in this meaning — an editor’s judgement
synonyms: send for, call
2verbgatherTo gather up a feeling or strength that does not come easily.
“He summoned the courage to knock on the door.”
formal in this meaning — an editor’s judgement
3verbspiritTo call up a spirit or creature by magic.
“The novel opens with a witch summoning something from the well.”
Also accepted in games: call
Summon travelled through Anglo-Norman somoundre and Old French sumundre from Latin summoneō, which is sub, 'under', plus moneō. That Latin verb goes back to a Proto-Indo-European causative built on *men-, 'to think': to make somebody think, to put a thing in their mind. What began as a quiet prompting from below now arrives as a court order.
Proto-Indo-European
*men- (think)
Proto-Indo-European
*monéyeti
Latin
summoneo
Old French
sumundre
Anglo-Norman
somoundre
English, today
summon
Built from
From Anglo-Norman somoundre, from Old French sumundre, from Latin summoneo, itself from sub + moneo, ultimately from Proto-Indo-European monéyeti, causative from men- (“to think”). Compare typologically from the same PIE root mention, Russian помина́ть, упомина́ть (developed less further, keeping strong relation with по́мнить), also compare помина́й как зва́ли (<+ звать).
Etymology from Wiktionary, CC BY-SA