"Seem unsteady on their feet", he adds (6)
I believe the answer is:
totter
'seem' is the definition.
Although both the answer and definition are verbs in their base form, I cannot understand how one could define the other.
'unsteady on their feet he adds' is the wordplay.
I cannot really see how this works, but
'on' could be 'to' and 'to' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for totter that I've seen before include "Proceed unsteadily" , "Stagger, reel" , "Move unsteadily; be about to fall" , "Walk unsteadily as if about to collapse" , "Wobble - rag-and-bone man" .)