(figuratively) to have sea legs; to be a good sailor

(takes a reflexive pronoun) to get up on the wrong side of the bed (to feel irritable without a particular reason)

ready to start work, ready to get down to business

on one level / walk-in / on an equal footing / directly, without transition

single-storey building / same-level apartment / one-floor residence / ground floor

(figuratively) thorn in the flesh, thorn in someone's side

to get out of one's depth (to get in a body of water too deep for one to be able to touch the bottom)

cheap shot (cowardly shot directed at someone who was once stronger than oneself but is now too weak to defend themselves, and whose weakness one takes advantage of to exact some sort of revenge)

on an equal footing, on equal terms

on an equal footing, on equal terms