Acquiesce
Etymology
From Latin acquiescere, "to come to rest, find peace in," from ad- ("to") plus quiescere, "to become quiet," from quies, "rest, quiet." To acquiesce is literally to settle into rest — to stop resisting and let a matter lie, which is why the modern sense carries that note of tired, wordless consent.
verb · /ak-wee-ESS/
To accept or comply with something reluctantly, but without protest.
What it names
The word for silent, passive agreement — going along with something you don’t love, precisely because you can’t be bothered to fight it.
Example
Rather than reopen the argument, she acquiesced to the new schedule with a small nod.
Related idea
Assent is active, positive agreement; to acquiesce is to agree only by declining to object.