Concentrated in a nervous way (7)
I believe the answer is:
intense
'concentrated' is the definition.
(similar in meaning)
'in a nervous way' is the wordplay.
I cannot really understand how this works, but
'in' is within the answer.
'nervous' could be 'tense' (similar in meaning) and 'tense' is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for intense that I've seen before include "Fervent" , "Extreme - strong" , "Strong in quality or degree - perhaps a feeling" , "Teen sin (anag.)" , "Strongly-felt" .)