of all meaning
EN- AdverbSUF-all
- Used as an intensifier with superlative forms of adjectives.
- Best of all was the bicycle I got.   First of all, I'd like to thank my agent.   He was the greatest playwright of all.
- Used as an intensifier with nouns to denote being ultimate.
- Of all the queer collections of humans outside of a crazy asylum, it seemed to me this sanitarium was the cup winner. […] When you're well enough off so's you don't have to fret about anything but your heft or your diseases you begin to get queer, I suppose.
- Used as an intensifier with superlative forms of adjectives.
- More Examples
- Used in the Middle of Sentence
- The English, of all classes, value themselves on this trait, as distinguishing them from the French, who, in the popular belief, are more polite than true.
- A large percentage of all Late Horizon fragments at this site was overfired, to the point where many were vitrified, black to dark brown, and misshapen, some with blistered surfaces.
- I could do without the CEO coming today of all days. I've got enough problems as it is!
- Used in the Beginning of Sentence
- Of all the inventors to obtain patents, only a few have really built a better mousetrap.
- Of all Infirmityes belonginge to us I hould those woorst that will not lett a man Rest in his bedd a-nights.
- Of all the Waldorf salads I've tasted, this is the finest.
- Used in the Ending of Sentence
- He is at most a confus'd and wild Christian, not specializ'd, by any forme, but capable of all.
- Used in the Middle of Sentence
Definition of of all in English Dictionary
- Part-of-Speech Hierarchy
- Phrases
- Prepositional phrases
- Prepositional phrases
- Adverbs
- Prepositions
- Prepositional phrases
- Prepositional phrases
- Phrases
Source: Wiktionary
Grammatically, this idiom "of all" is a phrase, more specifically, a prepositional phrase. It's also an adverb. It's also a preposition, more specifically, a prepositional phrase.