Bottom three frantic by end of season (6)
I believe the answer is:
nether
'bottom' is the definition.
(similar in meaning)
'three frantic by end of season' is the wordplay.
'frantic' indicates anagramming the letters.
'by' is a charade indicator (letters next to each other).
'end of' suggests the final letters.
The last letter of 'season' is 'n'.
'three' anagrammed gives 'ether'.
'ether' put after 'n' is 'NETHER'.
(Other definitions for nether that I've seen before include "These regions are beneath" , "Lower in position" , "Located below" , "inferior" , "North European country" .)