Thomas used some heady language (5)
I believe the answer is:
dylan
'thomas' is the definition.
Both the answer and definition are singular nouns.
Perhaps there's an association between them I don't understand?
'some heady language' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'DYLAN' is hidden in the letters of 'heady language'.
'used' is the link.
Can you help me to learn more?
(Other definitions for dylan that I've seen before include "Bob (musician) or Thomas (poet)" , "Bob --, US folk singer" , "Roundabout rabbit" , "and 19: Welsh poet" , "American singer-songwriter Bob, b. 1941" .)