Reliable cyclist ultimately out of practice (6)
I believe the answer is:
trusty
'reliable' is the definition.
(similar in meaning)
'cyclist ultimately out of practice' is the wordplay.
'ultimately' says to take the final letters.
'out of practice' becomes 'rusty' (synonyms).
The last letter of 'cyclist' is 't'.
't'+'rusty'='TRUSTY'
(Other definitions for trusty that I've seen before include "Staunch" , "Trainee officer" , "Reliable, well-behaved prisoners with privileges" , "Devoted" , "Reliable, faithful" .)