About this phrase

Lean is the second person, singular, imperative mood of the regular verb lean, meaning follow.

When it is used with the preposition ar, meaning on, it means continue, proceed with, persist in ⁊rl…

Thus, lean ort (literally, 'follow on you'): meaning continue / proceed / persist [in what you are doing].

Alternative forms

Lean ort is a common Connacht form.

Note that in Munster, lean is used with the preposition le, meaning with, to exactly the same effect. Thus, lean leat (literally, 'follow with you').