207. Certain numeral adjectives (single, double, triple, etc.) indicate how many times a thing is taken or of how many like parts it consists.
- A double row of policemen stood on guard.
- A fourfold layer of chilled steel forms the door.
Some of these words may be used as adverbs.
- The cabman charged double.
- His fear increased tenfold.
208. Certain numeral adverbs and adverbial phrases indicate how many times an action takes place.
- Once my assailant slipped.
- I rang the bell twice.
- The river hath thrice flow’d, no ebb between.—Shakspere.
The only adverbs of this kind in ordinary use are once and twice. For larger numbers an adverbial phrase (three times, four times, etc.) is employed. Thrice, however, is still common in poetry and the solemn style.