On terra firma, one can still be all at sea! (6)
I believe the answer is:
ashore
'on terra firma' is the definition.
(I've seen this in another clue)
'one can still be all at sea' is the wordplay.
I cannot really see how this works, but
'one' could be 'a' (a thing is one thing) and 'a' is located in the answer.
The remaining letters 'shore' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for ashore that I've seen before include "On land (as opposed to the sea)" , "Hoarse being no longer at sea" , "Hoarse (anag)" , "Toward land from water" , "in port?" .)