to examine, to consider, honest
諟 centers on careful mental engagement with truth: examining something closely, considering it thoughtfully, and acting with honesty.
諟 combines 言 (speech, words) with 是 (correct, right), suggesting the idea of examining words or ideas for correctness. The exact historical development is uncertain, but the component relationship is clear.
Words (言) and correctness (是) come together: imagine a scholar holding a magnifying glass over a written statement, checking every word to make sure it is right and honest.
For シ, picture a sheet of paper being examined line by line: sheet -> シ, and the careful inspection matches the kanji's meaning of examining and considering.