This is an arrayed formula so may slow down your workbook depending on how long your list is. Do not use A:A if possible use like A2:A200

=IF(MAX(--ISNUMBER(SEARCH($A$1:$A$100,B1)))>0, "Y","N")
...confirmed by pressing CTRL+SHIFT+ENTER to activate the array, not just ENTER. You will know the array is active when you see curly braces { } appear around your formula. If you do not CTRL+SHIFT+ENTER you will get an error or a clearly incorrect answer. Press F2 on that cell and try again.