TELL, v.t. pret. and pp. told. [L. telum; L.appello and peal, L. pello.]
10. To make known.
11. To discover; to find; to discern. The colors are so blended that I cannot tell where one ends and the other begins.
Tell, though equivalent in some respects to speak and say, has not always the same application. We say, to tell this, that or what, to tell a story, to tell a word, to tell truth or falsehood, to tell a number, to tell the reasons, to tell something or nothing; but we never say, to tell a speech, discourse or oration, or to tell an argument or a lesson. It is much used in commands. Tell me the whole story; tell me all you know, or all that was said. Tell has frequently the sense of narrate; which speak and say have not.
TELL, v.i. To give an account; to make report.
To tell of
To tell on - to inform. You must not disobey; I will tell of you if you do. This is a common popular use of the word. To tell on, is quite vulgar as well as improper.