good as (one's) word
Trustworthy, reliable, and will do what one has promised. If Bob said he'll be here at nine, then he'll be here at nine—he's good as his word. I was worried that Ms. Alberts would forget about her promise of no homework over the weekend, but she was good as her word!
good as one's word, as
Completely trustworthy, dependable, as in The boss said we could leave early on Friday and she was as good as her word. [Second half of 1500s]