Tell - definition of Tell from LearnEnglishIrregularVerbs.com

tell /tel/

1 to say something to someone, often communicating information, a story, your feelings, etc. or giving them instructions:
If your mother calls, tell her I'll be a little late.
Do as I tell you!
Tell Jane to bring the tea.
Like a general in the army she told him exactly what to do.
I told her that my heart was full of natural love for her, and that nothing could change that.
2 to give information in ways other than talking:
The light tells you when the machine is ready to be turned on.
Her eyes told him she was lying.
3 to know something or be able to recognize something by observing:
Turing had explained that if you had a long conversation with a machine, and you could not tell if it was a machine or a man, then the machine was thinking.
The mist grew thicker, and it was impossible to tell if the camera was seeing for ten centimeters or ten kilometers.