What does “Primi & imi, ad unum omnes” mean?

Question

From A vocabulary English and Latin:

67. Vapulabitis indiscriminatim omnes - You all, without discrimination, shall be beaten!

68. Primi & imi, ad unum omnes

The translation in the book is "High and low, not one shall escape", which seems fairly lax (as many other translations there). But I'm not sure how to understand this sentence (which is probably related to one above him). I have issues with both parts. Not sure whether primi and imi are nomanitive plural or genitive of something; also ad unum omnes is somewhat mysterious for me in this context.

Answer 1

Primus means "first," as you probably know. (Technically it is the superlative of prior.)

Imus is an alternative form of infimus, the superlative of infer, so it means "lowest," but also "last."

So I would say primi et imi means "the first and the last," but since this may also refer to positions (the ones in first place, the ones in last place), I suppose "the highest and the lowest" also fits.

Ad unum is a fixed expression meaning "to the last, to a man, without exception."

So I would translate the whole phrase as:

The highest and the lowest, no exceptions.