■ to assume that someone means, or will do, what he or she says.
- when he told her to go, she took him at his word and left.
- We had to take them at their word that the job would be done on time.
CF.■ my/his/your etc word: a sincere promise to do something, or a promise that what you say is true.
- I trust him to keep his word.
- I give you my word (=I promise) that it won't happen again.
- We only have his word for it that he has already paid.
- Delors claimed that Johnson had gone back on his word (=not done what he had promised to do).
- The business is doing very well. You can take my word for it (=accept that what I say is true).
- I never know whether to take him at his word (=believe what he says).
- His word is his bond (=he always does what he promises to do) .
.... Collins, WordNet, Macmillan, LDOCE