both

Từ điển American Heritage Dictionary 4th

both (bōth)adj.
One and the other; relating to or being two in conjunction:
Both guests have arrived. Both the books are torn. Both her fingers are broken.pron.
The one and the other:
Both were candidates. We are both candidates. Both of us are candidates.conj.
Used with and to indicate that each of two things in a coordinated phrase or clause is included:
both men and women; an attorney well regarded for both intelligence and honesty. [Middle English bothe, probably from Old Norse bādhar.] 
Usage Note: Both indicates that the action or state denoted by the verb applies individually to each of two entities. Both books weigh more than five pounds, for example, means that each book weighs more than five pounds by itself, not that the two books weighed together come to more than five pounds. Both is inappropriate where the verb does not apply to each of the entities by itself.·In possessive constructions of both is usually preferred: the mothers of both (rather than both their mothers); the fault of both (rather than both their fault or both's fault).·When both is used with and to link parallel elements in a sentence, the words or phrases that follow them should correspond grammatically: in both India and China or both in India and in China (not both in India and China).