To blow up is to explode, or to suddenly become very angry. Blow up the bridge, he blew up at me, blow up the photograph.
It also means to enlarge a picture and to inflate a balloon, which is a remarkable range for two short words. To blow up a story is to make it spread suddenly and everywhere.
1phraseblow upTo explode; also, to suddenly become very angry.
“The soldiers planned to blow up the bridge before the enemy could cross it.”
blow up is an exploding.
Middle English blow up is a rearranged form of the older upblowen.
Middle English
blow up
English, today
blow up
From Middle English blow up, blowe up, dissimilated forms of earlier Middle English upblowen (> English upblow), equivalent to blow + up. Compare West Frisian opblaze (“to blow up, inflate”), Dutch opblazen (“to blow up, inflate”), German aufblähen and aufblasen (“to blow up, inflate”), Swedish blåsa upp (“to blow up, inflate”), Icelandic blása upp (“to blow up, inflate”), Gothic 𐌿𐍆𐌱𐌻𐌴𐍃𐌰𐌽 (“to blow or puff up”).
Etymology from Wiktionary, CC BY-SA
Practised in Phrasal Verbs