Slow and dignified mythical ship at bottom of lake (5)
I believe the answer is:
largo
'slow' is the definition.
(similar in meaning)
'dignified mythical ship at bottom of lake' is the wordplay.
I cannot quite see how this works, but
'ship' could be 'argo' (I've seen this before) and 'argo' is present in the answer.
'lake' could be 'l' (geographical abbreviation) and 'l' is present in the answer.
No letters remain.
This explanation may well be incorrect...
'and' acts as a link.
Can you help me to learn more?
(Other definitions for largo that I've seen before include "Slow movement in music" , "at stately speed" , "Deliberately" , "major key" , "moving slowly" .)