Solution for 19 June cryptic crossword clue

Quite old, small tree on both banks of Liffey (7)

Solution – Elderly

"Quite old" = elderly – so that bit's ok

But what on earth has that got to do with an Irish river?  Actually nothing to do with the river as such.  "Both banks of Liffey" actually means the letters on each side (or "bank" if you will) of the word "liffey" ie ly.

If you add that to "elder" which is a sort of tree (usually a small tree) you get the solution.