Wiktionary
not to say
conj. 1 (&lit not to say English) 2 even; perhaps; almost.
Usage examples of "not to say".
It is at your disposal, which is not to say we should recommend your walking out on to the street with it.
Later still being frightened by a light footstep, furtive and sinister, until recalling that the crisp, not to say heavy step of officialdom would be more sinister.