Literally: connection / border – tree – request – fish
Alternately: An unreasonable or impossible implementation of a goal. A methodology so flawed that it cannot possibly succeed. For example, climbing a tree in order to catch fish. (Not in order to hang a fishing line or net into the water from, mind you: to catch fish in the tree.)
Notes: 縁 is the first character in the ゑ entries of all three traditional iroha karuta sets, so I’m guessing that classical orthography would render the modern “en” reading as ゑん here. This compound is certainly of sufficiently ancient lineage, apparently originating in one of the recorded dialogues between Mencius (of 孟母三遷 fame) and King Hui of Wei.
A more Japanese rendition of the same four characters, using kanbun reading, is 木に縁りて魚を求む (ki ni fuchidorite sakana wo motomu).