It's Apiaceae, a member of the carrot family. This was in a garden? That makes it a bit more difficult until it flowers.
Is the root edible? I’ve just planted it in a big flower pot. Shall I let it flower and collect the seeds?
Apiaceae contains some of the most poisonous plants known, so no, you wouldn't want to eat the root of an unknown member of the group. Was it from a gardening situation or was it collected elsewhere?